This seems to be a question not fully1 settled by sufficient authority. It seems as if this term were incorrectly applied2 and that suction would be a better name for the agency.
That bodies fall to the ground when dropped, or return when thrown or shot into the air is nothing more than a stick of wood thrown into a stream floats with the current and drifts to the bank.
Most people when asked which side of a fan you feel the air from, when fanning yourself, naturally reply from the side toward you, but by trying the experiment you will soon discover that the air comes after the passage of the fan, only filling the space or vacuum the fan has made.
It has often been asked why people trying to board a train in motion are so apt to be drawn3[82] under the wheels, and legs and arms crushed. It is the same reason as with the fan, a large vacuum is being produced and proportionate suction occurs to fill it.
A man can stand alongside a train when motionless and lean against it, or put his hand on it, as safely as on the depot4, but when in motion of thirty or forty miles an hour, it would be almost sure to cost him his life. Attraction can hardly be possible except by affinity5; iron can be attracted by a magnet no more than wood, unless possessed6 of that peculiar7 quality of being magnetic. Mr. Edison’s experiments have to be confined entirely8 to such bodies of ore.
That attraction of affinity exists there can be no doubt, as exhibited in plants, insects, birds and animals, both quadruped and biped, otherwise courtship and marriage and all means of propagating species would be for naught9 and neglected.
It is a general supposition that we derive10 our heat from the Sun by direct rays, but it is doubtful if it comes only through its innumerable rays of light through which the Earth and the planets revolve11, and here friction12 puts in one of its special works. The common idea that noon-day is the time for the greatest heat is not always justified13, for other influences, such as friction[83] in the atmosphere, can make midnight warmer than noon.
The concentrated rays of the Sun at midday of course bring them so closely together, and direct, that the Earth’s revolution comes squarely across them, as can be demonstrated across the teeth of a comb, thus showing a greater pressure than drawn obliquely14.
That heat can come directly from the Sun seems an impossibility without some medium of contact, which through the coldness and a barrenness ............