ON THE HISTORY OF HYDRAULICS, &c. 281 



It may be objected to Bernoulli's calculations, that some of the circum- 

 stances which are necessarily neglected in them, produce a very material 

 effect in the results of all experiments ; but it must be allowed that the 

 corrections required on account of this unavoidable omission, may easily 

 be deduced from simple experiments, and then applied to the most compli- 

 cated cases. It is, however, a more material objection, that the fundamental 

 law of the preservation of ascending force can only be adopted with certain 

 limitations ; thus, when a small stream passes through a large reservoir, Ber- 

 noulli is obliged to suppose the whole of its force consumed by the resistance 

 which it meets. The immediate mode, in which the accelerating forces must 

 be supposed to act, remains also wholly undetermined ; and it was princi- 

 pally for this reason, that John Bernoulli attempted to substitute, for his 

 son's calculations, a method of deducing the motions of fluids more imme- 

 diately from the gravitation of their different parts. The peculiarity of 

 John Bernoulli's mode of investigation consists in his imagining the weight 

 of each individual particle to be transferred to the surface of the fluid, 

 causing there a pressure in the direction of gravity; and he examines 

 the manner in which this force must operate, in order to produce every 

 acceleration which is required for the motion of fluids in vessels of all 

 imaginable forms. 



Maclaurm, in his treatise of fluxions, investigated several of the proper- 

 ties of fluids in his usual concise and elegant manner. His remarks on the 

 positions of the sails of windmills and of ships are peciiliarly interesting : 

 he added much to what had been done respecting the effects of the wind, 

 and showed the possibility of arranging the sails of a ship in such a manner 

 as to make her advance with a greater velocity than that of the wind itself. 

 At that time, however, the science of hydraulics had been too little assisted 

 by experiments to be capable of affording determinations of all questions 

 which are of very frequent occurrence in practice. An application was 

 made to Maclaurin, and at the same time to Desaguliers,* a man of con- 

 siderable eminence in the mechanical sciences, respecting the quantity of 

 water that might be brought, by a train of pipes of certain dimensions, to 

 the city of Edinburgh. The project was executed with a confidence founded 

 on their opinions, but the quantity actually obtained was only about one 

 sixth of Desaguliers's calculation, and one eleventh of Maclaurin' s. At a 

 still later period, the French Academicians were consulted respecting a 

 great undertaking of a similar nature ; and their report was such as to 

 dissuade the projectors from making the attempt, which was consequently 

 at the point of being abandoned, till a celebrated practical architect insisted, 

 from a rough estimation, deduced from his general experience, that more 

 than double the quantity assigned by the Academicians might be obtained ; 

 and the event justified his assertion. 



The experiments and calculations of Robins, respecting the resistance of 

 the air and the operation of gunpowder, deserve to be mentioned with 

 commendation on account of their practical utility ; but he appears to have 

 .been less successful in his theoretical investigations than Daniel Bernoulli 

 had been a few years before. 



* Robison's Mech. Phil. See Desaguliers's Course of Exp. Ph. vol. ii. p. 126. 



