MOTION, MECHANICS, ETC. 187 



Let a mass, 63m, be projected with a velocity of 11.877 

 inches in a second ; if it be resisted by a force equal to | m, 

 it will describe 21.95 inches in three seconds. To this end, 

 make A equal 2G m, and B equal 26^ m, and apply a flat 

 rod, 1^ m, to the upper surface of A ; set the circular 

 frame to 11.877 on the scale, then will A descend, the 

 moving force being m, and the mass moved equal to 65 m. 

 When it has described 11.877 inches, it will have acquired 

 a velocity of 11.877 inches in a second ; and the rod being 

 at that time intercepted, A will begin to descend with a 

 uniformly retarded motion, and will strike the square stage 

 set at 33.83, at the fifth beat of the pendulum, and thus 

 describe 21.95 inches in three seconds. 



For the account of various other useful and scientific ex- 

 periments, the reader had best consult the treatise of Mr. 

 At wood. 



This instrument has many other uses, which it is not 

 necessary to describe particularly here ; such as, The ex- 

 perimental estimation of the velocities communicated by the 

 impact of bodies, elastic and non-elastic ; The quantities of 

 resistance opposed by fluids, as well as for various other 

 purposes ; The motion of bodies, resisted by constant forces, 

 are reduced to experiment, by means of this instrument, with 

 as great ease and precision as the properties of bodies uni- 

 formly accelerated ; and, The verifying practically the pro- 

 perties of rotary motion. The two last are clearly shown 

 in Mr. Atwood's work. This very useful and illustrative 

 instrument requires to be well made, and nicely adjusted. 



The wheels and their mahogany bases can be separated 

 from their stand, and the various weights and other appa- 

 ratus, the scales, C, C : the ring, H ; the stage, D ; the 

 pillar, G ; and clock, E, are also made so as to be separated 

 and packed in a portable and convenient manner. 



Price, with clock, $100. 



