BOGTRINE OF PREPONDER ANCB. 59' 



X. 



A Defcription of Dr. Young's Apparatus for illvfirating the 

 Do6lrine of Preponderance *. Plate I. Fig. II. 



Although there can be no doubt of the truth of the ^;P|!!;^f "^' °/^^ 

 mathematical conclufions, which have been deduced from the mg the moft ad- 

 well known laws of motion, refpeding the moft advantageous vantageous em- 

 employment of force in machines, yet ihcy have, in general, ^^J^^^ 

 been too little confidered in pra61ical works, and fcarcely ever 

 enforced by experimental illuftration. The apparatus con- 

 trived for this purpofe, has been mentioned in the account of 

 (he leflures on mechanics ; its advantage is derived from ihe 

 Simplicity of its operation, and the facility of obferving at once 

 the feveral motions, which begin at the fame time, and may 

 eafily be compared, as long as they continue. The ratio of 

 the portions of the middle pulley, which is that of 5 to 2, is 

 near enough to the maximum (y^2 x 1) : 1 ; and the other 

 ratios 3 : 2 and 4 : 1 are taken fufficiently different from this to 

 (liow that the velocity of each is inferior to that of the middle 

 pulley. The pulleys are all perforated in the axis, and move 

 freely on a throng polithed wire, fupported by two (hort arras, 

 projecting a little from two upright pieces about three feet in 

 length, in order that the defcending weights may proceed 

 without interruption beyond the edge of the table. 



An Account of an Experiment on the Velocifj/ of Water fioxving 

 through a Vertical Pipe. By the fame Author. 

 IT has been alTerted by forae writers on hydraulics, and Whether the 

 y^enturi defcribes a particular experiment in fiipport of the J^j.^^. j|j.J|j j^ 

 afTertion, that the difcharge of water running out of the bottom a vertical pipe 

 of a ciftern, through a defcending pipe, is nearly the fame as^'°^jj;^^^^°'jj°"* 

 jf the ciftern were continued through the whole height, from the fame as 

 the furface of the water to the orifice of the pipe, and the^''°"J ^" '^^'^ '" 

 water were then difcharged from the bottom of the ciflern by total depth, 

 a fliort pipe in any diredion. The apparent difficulty of find- 

 ing a caufe adequate to the effedl, on the one hand, and the 



* In the leftures of the Royal Inflitution from whofe Journal 

 No, 1 1 . the prelent and next articles are taken, 



authority 



