CHAPTER V. 



THE PLANE-DROPPER. 



It is so natural to suppose that to a body falling in the air under the 

 influence of gravity, it is indifferent whether a lateral motion is impressed upon 

 it or not, as regards the time of its fall, that we may sometimes find in elemen- 

 tary text-books the statement that if a ball be shot from a cannon horizontally, 

 at any given height above the ground, and if a ball be dropped vertically at the 

 same instant with the dischai'ge, the two projectiles will reach the ground at the 

 same time, and like illustrations of a supposed fact which has in realit}^ no 

 justification in experience. According to the experiments I am about to describe, 

 this cannot be the case, although it requires another form of projectile to make 

 the difference in the time of fall obvious. 



It is shown by the following experiments that if a thin material plane be 

 projected in its own plane horizontally, it will have a most conspicuously diff"erent 

 time of falling according to the velocity of its lateral translation ; and this time 

 may be so great that it will appear to settle slowly down through the air, as it 

 might do if almost deprived of weight, or as if the air were a highly viscous 

 medium, the time of fall being (it will be observed) thus prolonged, when there 

 is no inclination of the plane to the horizon — a noteworthy and unfamiliar fact,* 

 which is stated here on the ground of demonstrative experiment. The experi- 

 mental quantitative demonstration of this important fact, is the primary object 

 of the instrument I am about to describe, used with the horizontal plane. It is, 

 of course, an entirely familiar observation that we can support an inclined plane 

 by moving it laterally deriving our support in this case from the upward com- 



* An analogous phenomenon concerning the movement of one soUd over another yielding one, such as when 



" Swift Camilla scours the plain, 



" Flies o'er the unbending corn, and skims along the main ; " 

 or in the familiar illustration of the skater on thin ice, ur in the behavior of missiles like the boomerang, has 

 long Ijeen observed ; and yet, remarkable as its consequences may be, these seem to have attracted but little 

 attention. Neither has the analogy which it is at least possible may exist between this familiar action of the skater 

 upon the ice and of the potential flying-machine in the air been genei'ally observed till lately, if at all — at least, 

 so far as I know, the first person who has seemed to observe the pregnant imi^ortance of the illustration is 

 Mr. Wenham, whom I have already alluded to. I do not, then, present the statement in the text as a fact in 

 itself unpredictable from experience, for it is a familiar fact that the air, like every material body, must possess 

 inertia in some degree. It is the quantitative demonstration of the extraordinary result of this inertia which 

 can be oVjtained with simple means in causing the thin air to support objects a thousand times denser than 

 itself, which I understand to be at the time I write, both unfamiliar in itself, and novel in its here shown con- 

 sequences. 



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