284 BULLETIN OF THE 



every spectator (himself included) in being swayed by a move- 

 ment as of assistance to the performer. In remarking tbe impres- 

 sion of being moved, while steadily watching a series of passing 

 canal boats, — on each boat reaching a certain point, he referred 

 the impression (amounting almost to a sensation of movement), 

 to the relative angle of vision formed by the moving body. 



He made a number of experiments on the flow of water jets 

 under varying conditions : also observations on sonorous flames 

 when passing into a stove-pipe of eight inches diameter and about 

 ten feet in length : on the comparative rates of evaporation from 

 fresh and from salt water: on the slow evaporation of water 

 from the end of a tube, and the much greater rapidity of evapo- 

 ration when the tube is open at both ends : extended notes of 

 which, with a great number of other researches, perished in the 

 flames. 



In 1844, he published a Syllabus of his Lectures at Princeton. 

 In December of that year he presented to the Philosophical 

 Society a communication of a somewhat more theoretical charac- 

 ter than usual, — on the derivation and classification of mechanical 

 motors. He refers these to two classes ; — the first, those derived 

 from celestial disturbance (as water, tide, and wind powers), — 

 and the second, those derived from organic bodies or forces (as 

 steam and other heat powers, and animal powers). The forces 

 of gravity, cohesion, and chemical affinity are not included, since 

 these tend speedily to stable equilibrium ; and they become 

 sources of mechanical power only as they are disturbed by some 

 of those before mentioned. It is not the running down of the 

 water-fall, or the clock-weight, which is the true origin of their 

 useful work, but the lifting of them up. The same is true of the 

 power derived from combustion. He then adds that his second 

 class (the forces derived from the organic world) might perhaps 

 by a similar process of reasoning be derived from the first class ; 

 (that of celestial disturbance;) — regarding "animal power as 

 referable to the same sources as that from the combustion of 

 fuel," and the action of the vegetative power as "a force derived 

 from the divellent power of the sunbeam," being simply a case 

 of solar de-oxidation. Organism — vegetable and animal, he con- 

 siders as built up under the direction of a vital principle, which 

 is not itself a mechanical force. Volcanic power is neglected as 

 comparatively feeble and limited, and not practically utilized.* 



* Proceed. Am. Phil. Soc. Dec. 20, 1844, vol. iv. pp. 127-129. Thi.s 

 appears lo be the first — as it is probably the best — analysis of physical 

 energy, which has been proposed. Twenty years later, a similar analysis 

 (with certainly no improvement in the classification) was adopted by 

 Prof. Tait, in an essay on '"Energy;" (North British Review, 1864, vol. 

 xl. art. iii. p. 191, of Am. edition:) and by Dr. Balfonr Stewart, in liis 

 Elem ntaiy Treatise on Unal, Oxford, 1806 (book iii. chap. v. art. 388, p. 

 354.) 



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