The Instrument Carriers wait till Monday to go back to Mr. Bryant's and pick up the Sector. "Not so bad so far, d'ye think?" Robert Farlow, who is driving the empty Waggon, remarks to Thomas Hickman, beside him.
"Not bad for Fields we've all work'd in forever." Hickman, who is receiving a shilling more than Farlow this week, bears a worried look. The other six-shilling man, Matt Marine, took himself off up the Bridge Road sometime in the Dark, and hasn't been seen since,— leaving it upon Hickman's shoulders to make sure no harm comes to the Sector. Behind them, back in the dust and wood-smoke, the ringing of ax-bits diminishes with distance. John Harland, and John Hannings, and Kit Myers recline in the Waggon-bed among the Cushions for the Sector, the ragged breeze of their Progress bringing them the pleasing Scents of the Spring-tide, as they roll along the New-Castle Road, two to three miles south of the Line, and roughly parallel to it. Overhead, Birds carry twigs to secret destinations. Beside the Road, Children come running to stare, caps askew, Forks and Churns left to lie. Farmers in Waggons coming the other way wave or sometimes, knowing who they are, glare.
Each time, they set out slightly to the North of West, upon a Bearing that will describe Ten Minutes of Great Circle before intersecting again the true West Line. The Gentlemen know from calculation that the Angle to be turn'd off must be 0°08'18" to the Northward of perfect West. For a while they take Sky Observations to confirm this, Dixon as if in defer?ence to Mason as Astronomer,— but presently they are turning the Angle directly from the Plate of the Instrument,— a Surveyor's habit, that Dixon may feel more comfortable with, which they drift wordlessly into, beginning to learn, each at his own rate, that the choice not to dis?pute oftentimes sets free minutes, indeed hours, otherwise wasted in issueless Quarreling. Neither appreciates this at the time.
When they reach the end of each twelve-mile-or-so segment, they stop, and set up the Sector, to find the distances, in Degrees, of several Stars, at their highest points in the Night, from the Zenith. Bradley's Star Catalogue gives the Declination, or Celestial Latitude, for each Star. This value, plus the Zenith Distance, equals the Earthly Latitude of the Observing Point.
Owing to the error in taking Bearings, that ever accompanies the run?ning of a real Arc upon the not quite perfectly spherickal Earth, the Sec?tor will never be set up exactly in the Latitude of the true Line. So Off-sets are figur'd at each Mile, ranging from zero at the eastern end, to whatever the difference in Latitude might prove to be, at the other. These offsets must then be added to the purely geometrical differences, at each Mile, between the ten minutes of Great Circle actually run, and its Chord,— the Line itself,— each time increasing from zero to about twenty-one feet at the halfway point, then decreasing again to zero.
As Fortune had put their first Ten Minutes of Arc close beside Octarara Road, so does their next Stage west allow them to set up the Sector but twenty-six Chains short of the east bank of Susquehanna, a mile and a half of Taverns strung near and nearer along the way up to the Peach Bottom Ferry. On Sunday the twelfth of May, they begin their Zenith Obs again, continuing them till the twenty-ninth. It will be a brisk and pleasant Fortnight beside the broad River, which dashes and rolls 'round two small Islands directly in the line of the Visto. On days of cloud, they endeavor to project the Line across the River, whose breadth they take the occasion to compute,— tho' the task falls mostly to Dixon, being, as Mason informs ev'ryone, more Surveyor's Work, really.
Dixon and Mr. McClean, along with Darby and Cope, go trudging down to the River to have a look. Common practice would be to measure out a Base Line upon the further Bank, set up there, turn off ninety degrees, put a mark on the near side, come back across, set up at the mark there, and find the angle between the two ends of the Base Line,—
 then, with the aid of a book full of logarithms, including those of "Trig" functions, 'twould take but a minute and a half of adding and checking, to find the distance across the River.
"That's how we learn'd in Durham," Dixon recalls, "to measure across places we'd rather not go. Not so much Rivers, of course, as unexpected patches,— sudden entire ranges of Spoil-heaps, or a Grove out in an empty Fell,— certainly nowhere near this d——'d many Trees."
"I've found little Joy in these Situations," offers Mr. McClean, whilst Darby and Cope nod at one another, silent as understudies in the Wings, moving their Lips no more than necessary. Sweating and muttering, all go tramping up and down the Bank, kicking up clouds of Gnats, crush?ing wild Herbs in Blossom, seeking a line of sight that will allow them to use a Right Angle,— a Fool's Errand, as it proves. At length, "Eeh, we'll have to use what Angles we can, then, that bonny with ev'ryone?"
And more than soon enough for the Chain-men, tho' Mr. McClean is shaking his head. "I never get the Figures right."
"Then let huz pre-vail somehow upon Mr. Mason, to review our com?puting,— Angles being the same,— so I surmise,— down here as Out There." Mr. McClean takes over the eighteen-inch Hadley's, and Dixon repeats his Sights with the Circumferentor, obtaining at last an ungainly Oblique Triangle, from which they calculate Susquehanna to be about seven-eighths of a mile across.
To Mason meanwhile has fallen the Task of projecting the Line across the River and setting upon its Western bank a point they might take up again from. Upon their last Saturday at Susquehanna, he writes, ".. .about sun set I was returning from the other Side of the River, and at the dis?tance of about 1.5 Mile the Lightning fell in perpendicular streaks, (about a foot in breadth to appearance) from the cloud to the ground. This was the first lightning I ever saw in streaks continued without the least break through the whol............