(C. Vincent Patrick)
A.—General Methods
The taking of spirit photographs under so-called “test conditions” has frequently been carefully investigated by men of high reputation in other walks of life, chiefly men of letters and men of science. In many cases they have been unable to detect any trickery, and after due consideration have decided that they know of no natural means by which the results obtained could be produced, under the conditions employed. This is in itself a perfectly fair conclusion; but it does not follow that because they know of no natural method, no such method
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 can exist; unfortunately the argument is frequently carried to this stage. Let us suppose that an eminent physicist watches a sleight-of-hand conjuror, who produces a dozen or more eggs from a small velvet bag, which was unquestionably empty when examined by the audience a few seconds previously; he will certainly not assume mediumistic powers on the part of the conjuror, or postulate the materialisation of a spirit hen. He realises that he is being deceived; he has had no training in conjuring, and does not know what to look for in order to “see through” the trick. How, then, does he expect to be able to detect a trick played upon him, probably in the dim light of a photographic dark-room, by a clever medium who has every method of trickery at his fingers’ ends? Even if he knew what to look for, the chances would be all in favour of the medium under the conditions which usually obtain; and in actual fact he probably has no idea of the multiplicity of methods which may be used for his deception. It seems therefore desirable to enumerate some of the many methods by which spurious spirit photographs may be produced. The following list makes no pretensions to being complete, but may give some idea of the variety of methods which the accomplished spirit photographer has at his service.
Group I.—Methods Involving Double Exposure and Substitution, in which a plate previously prepared with an undeveloped extra is substituted for the plate provided by the sitter. This gives excellent photographs, as the extra may be as distinct in detail as is desired, and the exposures can be calculated to a nicety, giving a suitably transparent spirit with a more solid portrait of the sitter. The substitution of the plate may be effected at almost any stage in the proceedings, for example:
(a).—Methods involving substitution of the entire packet:
1. The medium may be in league with the shop from which the plates are purchased, the unfortunate sitter buying a box of plates already prepared with spirits. Wise sitters buy their plates at a distance, but mediums frequently demand a particular brand of plate, and if those brought by the sitter are declared unsuitable, he will have to go out and purchase the correct ones. He is naturally supplied with the address of the nearest photographic dealer, and the name of the brand of plates is written on a slip of paper to show the shopman; this ensures no mistake being made.
2. If the sitter brings the right plates he will show the packet to the medium before entering the dark-room to make sure that they are all right. The medium takes the packet into his hand for a moment—turning to the light to read the label—and passes them back with the remark that they are the right kind—which now they certainly are, for the sitter’s original packet is in the medium’s breast-pocket.
3. The sitter may perhaps autograph or otherwise mark his packet
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 before coming to the medium, in order to prevent any such substitution. In this case the medium will wait until the wrapper is torn off in the dark-room, when he may be able to handle the box for a moment on some pretext,[4] and the dim light makes the substitution easier than before, particularly as it occurs during the first minute or so in the reduced light before the sitter’s eyes have become accustomed to it.
If these methods are employed, the medium usually finds it necessary previously to mark the plate or plates in the box that have the latent extras, in such a way that he may be sure of not getting the spirit inverted: a slight scratch on one edge will suffice for this.
(b).—Methods involving substitution of the faked plate only, after removal from the original packet:
1. With an unwary sitter this may be done in the dark-room. The sitter usually marks the plates; while he is marking one, the medium may be able to exchange his prepared plate for one of those not yet marked.
2. A trick dark-slide may be used, having a secret partition, and already containing the faked plate.[5] If the sitter is content to mark the plate after it is placed in the slide, he may easily be caused to mark the prepared plate instead of his own.
3. If the plates are not marked, it will be a simple matter to substitute, during the focussing operations, a duplicate slide containing a faked plate.
4. Little accidents are apt to happen in the unaccustomed light of the red lamp; while the sitter is groping on the floor for a wrapper he has dropped, or while his attention is in some other way diverted for a moment, the exchange is made.
I am aware that many will ridicule the idea of such a simple trick being played upon an intelligent observer; but any conjuror, whose business it is to do this kind of thing, knows that it is remarkably easy.
5. Sometimes the first photographs taken are blanks, the sitter then returns to the dark-room and loads up some fresh plates out of the packet. It may not occur to him that an accomplice of the medium has had access to the dark-room in the meantime, and when he gives this account of the séance a few days later he will probably have entirely forgotten that the plates were not all loaded at once.
Substitution can, of course, be effected in many other ways; every medium probably has his favourite method which he chiefly practises.
It may be pointed out here that in the case of a regular sitter who always marks his plates in the same way, as most do, it would not be
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 at all difficult to forge his signature on a prepared plate and substitute this for one of the marked plates.
Group II.—Other Methods, conveniently classified as follows:
(a).—Methods involving preparation of the studio:
1. An accomplice may be concealed behind the sitter, and be photographed with him; this is the simplest way of all, the sitter facing the camera, and, being told not to move during the exposure, is unaware that a “spirit face” is behind him, framed in an unsuspected opening in the background. Being behind the sitter, the face will be a little out of focus, and will appear rather blurred on the negative.[6]
2. It has been suggested that a mirror, or sheet of glass—on the principle of “Pepper’s Ghost”—may be introduced behind the sitter, producing the spirit by reflection of an accomplice hidden from the sitter. In practice this would be rather complicated and difficult to conceal; it would seem to have no advantage over the preceding method.
3. The extra is frequently sketched on the background—especially if this be a plain one—in some fluorescent substance, such as quinine sulphate. Such a sketch is invisible to the eye, but visible to the photographic plate. Many of Boursnell’s spirits appear to have been produced in this manner.
(b).—Methods involving the camera and dark slides:
1. A trick slide may be employed, in which the shutter contains a positive transparency of the desired extra, held in such a manner that it can either be withdrawn with the shutter, or left in position in front of the plate when required; i.e., during the exposure, which will have to be somewhat longer than usual.
2. A similar transparency may be inserted in the camera, close to the plate, and between it and the lens, during the focussing operations. The black focussing-cloth makes an admirable screen for such manipulations, while the sitter is of necessity immobilised a few feet from the camera. It is easy to imagine how a transparency on a spring mount could be slipped into the camera under cover of the cloth in such a way as to press up against the plate when the shutter of the slide is drawn.
3. It is stated that a doubly refracting lens has been used, focussing onto the same plate both the sitter and an object concealed at one side of the studio. Such a contrivance may have been employed, but would certainly not be cheap to manufacture.
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4. A simpler method of obtaining the same result is to have a pinhole in the bellows of the camera; a brightly illuminated object at the side and rather in front of the camera will then throw an image on the plate. A considerable exposure will be needed to give a fair extra; but this will present no difficulties, as the pinhole will be open all the time the plate is in position, and not merely during the few seconds that the lens is uncapped for the photograph of the sitter.
5. An extra may be painted on the inner surface of the dark-slide shutter, in some radio-active chemical. The shutter usually only clears the surface of the sensitised emulsion by a fraction of a millimetre, and a fairly distinct extra will be produced if the plate is kept in the slide for a sufficient length of time—depending, of course, upon the amount of radio-active substance used.
(c).—Dark-room methods.
1. In the days of the wet-plate process, when plates were cleaned and used a second time with fresh emulsion, it would sometimes happen that the original photograph would re-develop on top of the second, very careful chemical cleaning of the plate being necessary to prevent this. Mumler’s first spirit photograph was probably produced in this way, and the knowledge was turned to good account by several of the earlier spirit photographers. Some of the unexpected results obtained by amateurs may be attributable to this cause, because a certain number of used plates are returned to plate manufacturers, who clean off the emulsion and use the glass again. The cleansing may sometimes be imperfect, and in these cases the original image may appear on development.
2. Faces may be sketched in chemicals on small pieces of card, or even on the medium’s fingers. On opportunity arising in the dark-room, the medium holds or steadies the plate for an instant, bringing the chemical pictures into contact with the plate. Or he may so manœuvre it that the plate is laid face down on a prepared surface of the dark-room work-bench, probably while it is being marked[7]; upon development of the plate extras will duly appear. The most refined version of this method consists in the preparation of small rubber stamps in which the chemicals are smeared. These can easily be palmed and dabbed for a moment on the plate in a manner which appears quite unsuspicious. A number of active chemicals will produce this effect, but the medium must be careful to know whether the substance he is using will accelerate or retard development in the affected part; for cases have occurred in which a positive extra has been produced on the negative plate, giving a negative spirit on the finished print!
3. Mr. Bush, in his recent pamphlet, “Spirit Photography Exposed,”
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 describes a piece of apparatus made out of an empty blacking-tin containing a small electric bulb, one side of the tin being replaced by a positive transparency of the desired extra. This, he alleges, is used by Hope, the Crewe spirit photographer, the transparency being pressed against the plate and the light switched on for a second. If carefully faced with black velvet round the transparency, this device should be quite useful; but it must be remembered that an escaping ray of white light would at once catch the eye in the dark-room. Skilful palming and manipulation should make it quite possible for an extra to be printed on the plate in this way, if the medium can cover it with his hand for a moment or two. All Hope’s results are certainly not produced in this way, however, as is implied by Mr. Bush.
4. The medium may palm a positive transparency; if he is allowed to handle the plate he will hold it close to the red lamp with the transparency between; if the lamp is rather bright, or is not a very deep red, an impression is soon made on the plate.
5. With a pinhole in the dark-room lamp, and a transparency inside—a perfectly practicable arrangement with some of the more complicated dark-room “safe-lights,”—a pinhole projector can be formed, which will throw an image on a suitably-placed plate. Any leakage of white light into the dark-room, either from the lamp or from outside, can be used to produce blotches and streaks on the plate. A very little mechanical ingenuity will enable a medium who takes a pride in his work to rig up an arrangement of this kind which can be switched off and on at will and which will project an image on a predetermined spot on the bench. By the simple expedient of having the bench so cluttered up with bottles and miscellaneous rubbish that this spot is the only unencumbered one, the unsuspecting sitter may be forced to lay a plate on this spot while, for example, he is marking another. The medium may ostentatiously stand at the other end of the room and “switch on” for a moment while the sitter’s attention is engaged with his marking.
6. Photographic plates are sensitive to rays invisible to the eye, as has been pointed out in considering the effect of fluorescent substances. X-rays and ultra-violet rays, for instance, both invisible yet strongly actinic, might be used in the most baffling manner in the production of spirit extras. The expense and technical difficulties would be considerable, but were any medium to take the method up, he might safely defy the most critical investigation and would soon recoup himself for the few pounds initial outlay.
There are undoubtedly many other methods used by mediums for this purpose; but if the sitter who has obtained spirit extras under test conditions carefully considers the procedure employed, in the light of the suggestions made above, he will probably find that several loopholes were left by which fraud might have been introduced.
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B.—Experiments in Fraud
The argument most frequently brought forward, in favour of the genuineness of spirit photographs, is that the conditions employed in their taking leave no loophole for fraud. It has been pointed out in the preceding section that the usual “test conditions” leave not one, but many, such loopholes. Evidence of fraud has at some time or other been brought against most spirit photograph mediums, and they have consequently been more or less discredited. Other mediums have been more clever—or more fortunate—and many people therefore argue that they are not all to be tarred with the same brush; it is pointed out that spirit extras have been obtained under the strictest conditions imposed by acute observers who have found nothing suspicious of trickery.
It occurred to me that the most effective way to refute this argument was actually to produce bogus spirit photographs under similar, or even more stringent, test conditions. This I accordingly attempted in a series of séances, held in my rooms at Cambridge in the summer of 1919. At four of these séances photographs were taken, and on each occasion one plate showed a more or less conventional spirit extra. As I was experimenting primarily for my own satisfaction, my seven victims were drawn from among my own friends, and were enjoined to keep the matter as quiet as possible. They were not, of course, specially trained psychic researchers, but could not, I think, be considered as being particularly easy men to deceive. Five of the seven were ex-Service men, and all were of B.A. or “fourth year” University status; they included two chemists, two medical students, a geologist, and two physiologists who were also studying psychology. They were all therefore of a scientific bent, and, with possibly one exception, were completely sceptical about spiritualistic phenomena when the experiments started.
I first suggested to four of them that we might try to obtain a spirit photograph, like those described and reproduced in recent magazine articles. They did not take me very seriously at first, but after we had obtained the right atmosphere with a little table-turning, they consented to try for a spirit photograph. When a spirit face duly developed in addition to the sitter, everyone present expressed amazement! I was naturally asked if I was “pulling their legs.” I hedged and refused to say either yes or no, explaining that I wanted the experiments to continue under scientific conditions. If, on the one hand, I declared that I had not in any way faked the photograph, they would probably believe me, and would not insist on further photographs being taken under test conditions. If, on the other hand, I refused to give such an assurance, they would think that I was probably tricking them, and would take all possible steps to “bowl me out”;
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 and when they failed to do so would thereby establish evidence of the genuineness of any further photographs we might be lucky enough to obtain. After some little demur they saw the point of this—or as much of it as I wished them to see—and agreed to meet again in my room on the following Sunday evening, promising that I should be given no opportunity of playing any tricks. It was also agreed that notes should be taken during the séances as far as possible, and that full reports of what occurred should be drawn up afterwards by all of us in conjunction, which everyone would sign.
I now quote their report on the next two meetings, omitting nothing except their names, which I have replaced by single letters, at their request.
“On the following Sunday, July 20th, at 8.15, there met in Patrick’s rooms A, B, C, and D. Saturday being a Bank Holiday, the plates were purchased on Friday evening by B, and kept by him until the meeting. B produced his plates, unopened, and after some preliminary table-turning and rapping, more successful than at the previous meeting, it was decided to proceed with the photographs. A carried the plate-box unopened to the dark-room, and he and D sat closely on either side of Patrick, and watched him open the box and load two double dark-slides; they were satisfied there was no substitution or trickery, or anything in the least degree suggestive of it. The wrapper of the box was broken in full view of both, and Patrick loaded the top four plates into two double dark-slides, which were examined by A and D immediately before they were loaded; they did not leave their sight from the moment of examination until the photographs were taken. The camera was also subjected to careful and minute examination, especially by A, who removed the lens and examined both it and the interior of the camera. The lens was then replaced, and the focal plane shutter set in the open position, the exposures being made by the simple expedient of withdrawing the shutter of the dark-slide.
“At the request of C, before approaching the camera to focus it, Patrick removed his coat, rolled up his sleeves, and was carefully searched by him.
“It had been arranged that Patrick should take a photograph of each of the four others present, under identical conditions. The background was arranged, as before, of gowns hung over a cupboard, but was made more complete. The subjects occupied the same chair in succession; of the others, one stood by the light switch, and the two others by the camera, to watch the photographer. Patrick attended both to the camera and the flash production. The exposures were made, as stated, by withdrawing the shutter of the dark-slide; the focal plane shutter was not touched throughout. The electric
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 light was therefore switched off for a few seconds while the shutter was drawn and the flash being lighted. Sufficient light came through the white window-curtains (9.30 p.m. Summer Time) to enable those in the room plainly to see each other, and watch the photographer’s movements. The four photographs were taken in rapid succession.
“The slides were taken back into the dark-room, and developed by A and Patrick in conjunction. B and C watched in turn, and D also watched part of the time. One of the plates was quickly observed to have an ‘extra’ developing on it. A bromide print was again taken from the wet negative, and showed on the photograph of D the head of an elderly man, besides a very fair photograph of the sitter. The extra face was above D’s head, and to his right. The “spirit” was bearded, and partly bald, with a somewhat melancholy expression. There was a suggestion of a white collar. On the left of the face and somewhat above it was written in white on the black background what was apparently a signature, with two final letters of a preceding word. It was dubiously deciphered as ‘...ly S. Simmonds.’ Neither face, name, nor writing were recognised by any one, either at the time or subsequently.
“The three other photographs were fair portraits, but showed no abnormality.

“A third meeting was held in the same place at 8.15 p.m. on Sunday, July 27th, when even more stringent conditions were imposed on the photographer.
“The plates were bought on Saturday evening by D; other men should have been present, but did not turn up at the arranged time. D took the plates to his own rooms, where Patrick sealed them for his own satisfaction. The box was kept locked up by D till he brought them to the meeting on Sunday, and he did not part with them till he gave them to E to take into the dark-room.
“At this meeting there were present A, B, C, D, E, F, and G, besides the photographer.
“When all had arrived, E carried the plates to the dark-room. C brought a dark-slide, which he had abstracted and kept since the previous meeting. Before going into the dark-room Patrick, again at the request of C and E, removed his coat, rolled up his sleeves, and was searched, C even going to the length of examining his socks for possible concealed plates or dark-slides.
“Patrick wished to load the slides himself, as they were rather delicate. Accordingly neither slide nor plates were passed into his hands until he was sitting in front of the ruby light, with E on one side of him and C and F on the other. He broke the seals, and in full view of these three loaded a single plate into compartment No. 3 of the dark-slide. This was then immediately taken from his hands
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 again by E, and he and C locked it in a drawer of the desk, upon which stood a reading-lamp, which was never extinguished throughout all the subsequent proceedings. C kept the key of the drawer, and passed it to E when the slide was required.
“Some table-tilting was then carried out by all except C, who remained at the desk and acted as secretary. The lights were all put out except the reading-lamp he used, which was, as stated, over the drawer where the dark-slide lay locked.
“After half an hour or so of moderate success with the table, E and Patrick also dropped out, to take a flashlight photograph of the group round the table. Patrick prepared the flash-powder, and set up the camera—which had previously been examined—by the side of the desk and lighted lamp. E again examined the camera, inside and out, and when Patrick had focussed it examined the view in the ground-glass screen. (The lights were put up for a few minutes, to aid the focussing, etc.) When all was ready, E received the key from C, unlocked the drawer, and took out the dark-slide. He saw that it was undoubtedly placed in the camera right way about, i.e., No. 3 compartment in use, and the shutter withdrawn. When the table had commenced its tilting again the flash was fired by Patrick. C took notes of the movements of the table, and at the same time watched the camera, which was in the full light of the reading-lamp throughout. After the flash the shutter of the slide was replaced, and on removal from the camera the slide immediately passed again into the possession of E. Any substitution of plate or dark-slide was thus rendered out of the question.
“The dark-slide was taken to the dark-room by E, and he and C watched Patrick open it, remove the plate, and develop it. As before, E kept the slide till everything was ready, and passed it to Patrick in the full light of the ruby lamp, C checking the number of the compartment in which the plate had been loaded, and still remained (No. 3). On development, Patrick pointed out that there was a hand at the top of the plate, which could not belong to any of those at the table, and was pointing with its index finger at one of the group. On fixing, it was examined more closely, both by Patrick and the two others. All three distinctly saw the image of a hand and wrist, pointing, the forearm being draped. It was in fairly sharp focus, and appeared, by its proportion, to be rather nearer the camera than the centre of the table, above which it appeared to hang suspended. A shadow cast by it was plainly seen, larger and less sharply focussed, apparently on the back wall of the room. (A picture on this wall had previously been removed, to eliminate any reflection, and leave the background clear.) There was a general appearance of drapery surrounding the group, particularly at the sides; there was in this the suggestion of a trunk to which the hand might belong. The appearance of the picture
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 was very startling, and Patrick suggested that as the man at whom it should turn out to be pointing might suffer considerable uneasiness on seeing it, it might be well to destroy the plate without attempting to identify him. E and C, after a minute’s thought, both agreed that this would be the wisest course, and it was accordingly done. Patrick did not wish to feel that he might be in any way responsible for causing anyone uneasiness or harm, such as might well result from such a picture.[8] Accordingly the three returned to the other room, and explained the situation to the others, who, though obviously disappointed, did not condemn the course taken.
“This concludes the account of these first three meetings. We wish to record that all through the meetings Patrick desired and requested us to take all and any precautions we thought fit, to satisfy ourselves that he introduced no trickery.
“In conclusion, we, the undersigned, declare this to be an accurate account of the occurrences to the best of each man’s individual knowledge. While not committing ourselves to any statements as to our belief or disbelief in the genuineness of the phenomena observed, we maintain that the greatest possible care was taken to prevent any possibilities of trickery; and we consider that, barring the possibility of Patrick having an accomplice among us, the evidence should be accepted as proof of the genuineness of the phenomena observed.”
This is followed by their seven signatures. E added afterwards a paragraph of his own as to the interpretation of the word “accomplice.” E was much the acutest observer and the most obstinate sceptic of the seven: I think he suspected D of being in some way my accomplice; some of the others suspected him of being a medium. He certainly was not an accomplice—for I never had one in the room; he may be a medium for aught I know—but I should doubt it.
At the next meeting an eighth investigator appeared, and everybody seemed to be suspecting everybody else, and not merely the photographer. The plates were bought at a different shop, chosen by lot, by a committee of four; and the packet was at once done up with much red tape and green sealing-wax. When they had finished I requested to be allowed to put my seal on it too, to assure myself that they were not playing any tricks! My request was granted. I now quote the report of the meeting:
“The box of plates was produced by C, and the seals were found to be intact. The box was taken into the dark-room by A, and a plate-carrier—which
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 had been previously examined by several of those present—by B. The seals were broken, and a plate was loaded in the presence of A, B, D, and E, who signed their names on stamp-paper fixed to the back of the plate.
“In attempting to fit the slide into the camera, the plate was accidentally exposed. It was discarded, and another plate signed and loaded by A, C, E, and Patrick. C then locked the plate away in a drawer, and kept the key until the slide was required for the photograph.”
[Table-turning was then indulged in; A, C, E, and myself not taking part. The usual type of answers was obtained from the table; I omit this part of the report. During the table-tilting the photograph was taken under precisely the same conditions as at the last meeting.]
“The plate was developed by Patrick; A, C, and E watching. An extra pair of eyes and the upper part of a nose developed, apparently on the wall; they were brightly illuminated, from the same position as the other figures. They were larger than those of the other members of the group, and were over B’s head.
“We consider that this is a true account of what occurred. Barring any very abstruse and elaborate explanation, it would seem that the photograph is undoubtedly genuine.”
Then follow the signatures. As they made me sign the report on this meeting, I had to see that it was worded rather carefully, particularly the last paragraph; the report was true, so far as it went; and the explanation of the result was rather elaborate; so I felt I could safely sign it.
I did not hold another photographic séance, but being emboldened by success, introduced at the next meeting “a medium from London.” (As a matter of fact he came from Trinity, but I had ascertained that nobody knew him, which was the important thing.) After suitable preliminaries we all sat round a large table in semi-darkness, holding hands. When the medium had arranged “the balance of the circle” to his liking, he proceeded to go into a trance, when queer things began to happen. A candlestick was seen to slide along the mantelpiece and crash into the coal-box, taking a framed photograph with it; sounds were heard from a small cupboard; the window-curtains were parted; several people saw spirit forms and eyes; and one was favoured with a spirit touch. The medium’s Egyptian control, Nemetra, gave us wonderful accounts of life in Memphis in the days of the Pharaohs—accounts which certainly made up in picturesque detail for anything they lacked in historical accuracy.
Unfortunately this meeting was not a complete success, as, immediately the show was over, our ever-curious geologist E began hunting about the floor, and discovered a small loop of fishing-line (being a post-war fishing-line, the spirit forces had broken it). He
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 could not very well announce his find at the time, as the medium was not yet roused from his trance, and the others were busy feeling his pulse, fanning him and administering cold water!
By this time the results of the photographic séances had become pretty generally known, and the undesired notoriety brought so many requests to allow other visitors at the séances that it became evident to me that the proceedings must terminate. So the next morning, after seeing E, I told him and the others that the whole thing had been a hoax, and that the photographs were frauds. I should like to add that with one exception they took it extraordinarily well, particularly when I explained what had been my object. They were still quite in the dark about how the photographs had been done, particularly when I told them that there was no accomplice among them.
All the photographs were obtained by the general method of double exposure and substitution, the substitution being effected at a different point on each occasion; the methods used, or slight variations of them, are all described in the section on “Methods of Fraud.”
Now I maintain that the conditions imposed upon me were as strict, or stricter, than any professional medium allows. If an amateur photographer but little practised in sleight-of-hand can under such conditions deceive intelligent observers—not once, but several times over—how much easier will it not be for the professional spirit photographer, who makes such frauds his business?
C.—Internal Evidence of Fraud
Since spiritualists claim that the presence of invisible spirits may be detected by photography, it seems reasonable to inquire how far this is compatible with established physical facts. If a plate is wrapped in paper and submitted to “spirit influences”—whatever these may be—never being exposed in a camera at all, and on development shows faces or writing, I personally can only find one explanation—trickery. But if a plate is duly exposed with camera and lens, and unseen faces appear on development, the matter is not quite so simple. For it is well recognised that the camera may record what is invisible to the eye; invisible stars are detected by the photographic plate, and anyone who has examined a nebula or comet through a telescope, after seeing a photograph of the same object, realises this fact to his disappointment. Similarly a can of hot water may be photographed, by a long exposure, in a perfectly dark room; and another well-known instance of a similar phenomenon is Sir Robert Ball’s story of photographing some writing on the side of the “Great Eastern,” years after it had been painted out and rendered invisible.
Light, as is well known, is now regarded as consisting of waves in the ether. Ether waves are known to exist over a very large range of
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 wave-lengths; some are comparatively long waves, some are short. The properties of these waves depend upon their wave-length; those visible to our eyes, which we call “light rays,” form only a small section of the complete scale; comparing them with sound waves they correspond to approximately one octave of the whole musical scale. Ether waves of greater or lesser wave-length than light, i.e., of lower or higher octaves, have very different properties. Radiant heat and ultra-violet rays are the ether waves nearest in wave-length and properties to light; X-rays and the waves responsible for wireless telegraphy appear to be similar waves further removed along the scale of wave-length.
Now in order to photograph an invisible object we require rays that (a) affect a photographic plate; (b) are capable of refraction by a lens; and (c) are invisible to the eye. The properties of the principal known rays concerned may be summarised as follows:
 
Effect on Plates
Refracted by Lenses     
Visibility
Infra-red (heat) rays  
v. slight
Yes
No
Light rays
affected
Yes
Yes
Ultra-violet rays
strongly affected   
Yes
No
X-rays
affected
No
No
It appears, then, that ultra-violet rays are suitable for our purpose; infra-red rays, if present in an amount sufficient to affect a photographic plate, would make themselves very evident as heat, and may therefore be ruled out.
Ordinary daylight contains ultra-violet rays, as also does the light of the arc lamp and magnesium flash; lamplight, gas-light, and the ordinary electric light, are comparatively deficient in them. But are we to assume that the spirit form is dependent on finding suitable rays in the surrounding ether, or can it produce its own? Perhaps some spiritualist will tell me. This is a point of some practical importance in examining a reputed spirit photograph; for if the spirit is self-luminous its features will be evenly illuminated and without shadows, nor will it cast a shadow on the sitter or background, but rather the reverse. If, on the other hand, the spirit is dependent on the presence of ultra-violet rays from other sources, which it can reflect, then the spirit in the photograph will appear to be illuminated from the same point as the sitter,[9] and by absorption or reflection of the ultra-violet actinic rays which would otherwise have passed on, will cast a shadow on the background. Being a shadow cast by the
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 removal of the ultra-violet rays only, it will of course appear as such in the photograph, but be invisible to the eye.
So if a spirit photograph is to be classed as possibly genuine, the spirit may either appear self-luminous and cast no shadow, or may appear to be illuminated from the same point as the sitter, and cast a shadow on the background, if the latter be of a suitable nature to show it. But on examining a collection of spirit photographs taken by various professional mediums, we find that as often as not the spirit and sitter are lighted from opposite sides; or that a spirit face with a well-marked shadow on one cheek throws no shadow on the background. If our reasoning be correct, we can at once write such productions down as frauds. The photographs I produced at my Cambridge séances show both these faults; two of them have the spirits lighted from the opposite side to the sitter, and one has the spirit lighted from the correct side but throwing no shadow, whereas the sitters throw clear shadows on the wall behind. In the other photograph I managed to get both the lighting and the shadow of the spirit correct; but in order to get the shadow I had to photograph the background with the “spirit”; hence when the sitters were photographed on the same plate there was a double background, which necessitated a rapid destruction of the plate!
Of course the average medium does not consider these points at all; his sitters are usually satisfied with anything they can get, so why should he worry? But an intelligent observer examining a number of spirit photographs with regard to these points will quickly satisfy himself that the majority of them can only be frauds.[10]
There are a number of other points by which a spirit photograph may betray its method of production without reference to the conditions under which it was taken. Many spirit extras are simply copies of existing photographs, which are usually camouflaged in some way. Draperies may be substituted for the hair, or the features slightly retouched. A common method is to reverse the original photograph, right for left; a number of Hope’s productions were recently published in a monthly magazine, and alongside them life portraits of the “spirits,” the letterpress emphasising that, though undoubtedly the same face, they were different photographs. On examination with a mirror, however, the photographs were seen to be identical, and careful measurement of the faces showed the proportions to be exact. In the
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 photographs more recently published by Mr. Bush, who laid a trap for Hope into which the latter appears to have fallen, the spirit was not reversed, nor was even the rather peculiar attitude of the head in the original photograph altered. A little spirit drapery was added round the face, and the whole thrown slightly out of focus; it is really a most clumsy piece of work, and should deceive no one.
In some spirit photographs produced by double exposure there is a double background, as occurred in my own photograph referred to above. There may be either two different backgrounds, or a double outline of the same background; in either case the “spirit’s background” is usually fainter than the “sitter’s background,” and shows through the darker parts of the sitter. Sometimes attempts are made to retouch these appearances on the negative, and many spirit photographs show clumsy brush or pencil work, which must immediately stamp them as frauds.
Attempts are sometimes made to obliterate other tell-tale marks, such as a piece of a spirit’s hat or collar, which has accidentally got on to the plate. Other mediums, however, are less particular, especially in America, and produce their spirits with ordinary hats, collars and ties. But as a rule only spirit robes are permitted, apparently made of butter muslin not quite in focus. Hands are often present: I have seen a case in which the position of a spirit hand would have necessitated a many-jointed arm about four feet long; but perhaps spirit arms are like this. One spirit extra I have seen has two hands, but both appear to be left hands—evidently a left-handed spirit.
Frequently, again, careful examination shows that spirit extras are not photographs at all, but resemble wash drawings. This gives the clue to their origin, for several of the methods described in a preceding section produce a result of this kind. It has been several times pointed out that spirit extras in some cases show the characteristic dots produced by the half-tone newspaper illustration process; if the medium cannot obtain a real photograph of the required spirit, he has to copy a newspaper reproduction. If he is clever, he can eliminate these process marks by printing in his spirit slightly out of focus; but very often he does not take the trouble.
In many, perhaps in the majority, of spirit photographs produced by professional or semi-professional mediums, a critical observer with practical photographic experience can point out some such definite evidence of fraudulent manipulation. In many other cases, where no one particular point can be singled out as indicative of fraud, minor points of suspicion are noticeable, which taken together leave little doubt of the nature of the picture. But photographs can be prepared by purely mechanical means, especially if no kind of test conditions are employed, which will contain no internal evidence whatever of manipulation. By carefully combining enlarged positives, for instance,
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 and re-photographing the whole, results can be produced which will defy the most critical examination. But such photographs are seldom produced, even when the medium is given practically a free hand.