178 Mr. J. J. Waterstone's Exposition of 



approaching the asymptote m n, which is parallel to ab; their 

 mutual distance avi being proportional to the density of the 

 fluid at an infinite distance from a, or to every part of it be- 

 foi'e the introduction of the rigid plane. 



III. Let a second rigid plane be introduced and placed at 

 a distance from the first, indefinitely greater than the extent 

 of its longitudinal dimensions. What are the effects conse- 

 quent on this arrangement? 



Let A B be the relative position of the two planes, which 

 let first be considered parallel, and intersected by a common 

 perpendicular A B. Let « A, /3 B, represent 

 their indefinite extension. The rareness of ^ 



the medium occasioned by the impulsive force j^ 



radiating from the plane being proportional « 

 to the quantity of rectilineal force exerted 

 amongst the particles in the same space, and 

 the sums of the intensities of the rectilineal 

 motion proceeding from both planes being 



greater in the interior space AB than in BC n 



A D, on the exterior sides, it follows that the \^ 



medium will be denser in the latter than in c 



the former, and more particles 'will thus im- 

 jnnge in the same time on the exterior than on the interior face 

 of each. The equilibrium which kept the first plane at rest 

 before the introduction of the second will be therefore de- 

 stroyed, and a motion communicated to each, which will cause 

 them mutually to approach with an accelerating velocity; 

 and this by the decomposition of forces will likewise take 

 place at whatever angle the particles are inclined to each other. 

 Thus the effect consequent on this new arrangement 'will he the 

 development of a mutual attractive force. 



Observations. — The foregoing principle is founded on a 

 simple mechanical effect, which may be made the subject of 

 experiment. Take a small glass cylinder, suspend it by a fine 

 thread, and communicate to it a spinning motion round that 

 centre. Bring it now gently in contact with a glass plate ; the 

 instant that collision takes place the cylinder will be thrown 

 from the plate with considerable violence, whilst its revolving 

 motion will have almost totally disappeared. This experiment, 

 which is easily performed, corroborates what is mentioned in 

 the first part of Article IL and affords a satisfactory proof of 

 the efficacy of the general principle. As a corollary to Articles 

 IL and III. we have to observe, that if the finite particles 

 were rigid planes of uniform thickness, the attractive power at 

 the same distance would be proportional to the extent of sur- 

 face ; in other words, to the quantity of matter contained in 



the 



