396 Prof. De Volson Wood on 



the limit of the capacity of the pumps ; and Professor Rood 

 produced one of 390 q 000 of an atmosphere* without passing 



the limit of action of his apparatus. The latter gives a 



, 14-7x144 x ' 



pressure per square foot of 39Q 0Q0 0Q0 = i^oob of a pound. 



This, in round numbers, is 140 times the value given in equa- 

 tion (11). Even at this great rarity of the atmosphere, the 

 quantity of matter in a cubic foot of the air would be some 

 200 million million times the quantity in a cubic foot of the 

 aether — such is the exceeding levity of the aether. 



Admitting that the aether is subject to attraction according 

 to the Newtonian law, and of compression according to the 

 law of Mariotte, we propose to find the relation between the 

 density of the cether at the surface of an attracting sphere and 

 that at any other point in space, providing that the sphere be 

 cold and the only attracting body, and the gas considered the 

 only one involved. 



Let S , e , w be respectively the density, elasticity, and 

 weight of a unit of the medium, whether aether, air, or any 

 other gas, at the surface of the sphere; S, e, w, the corresponding 

 quantities at a distance z from the surface of the sphere; r the 

 radius of the sphere, g the acceleration due to gravity at its 

 surface, and g that at distance r + z from the centre of the 

 sphere. Then 



8 e w m w 

 So ~~ e "" g g 



and 



ff=9o- 



But 



(r+zf 



e=*.*>w=^^w. . . . (12) 



w g w r z v y 



de=—wdz=—g$dz; .... (13) 



. de __ g S r 2 



— — • : — ; — r« az. 



e e (r + z) 2 



Integrating between e and e , r + z and r, we have 



e = e € e 'r+z y (14) 



_g_o$o _™_ 



S = 8 6 *o 'r+Z ( 15 ) 



Neglecting the attraction of ihe earth for the aether, and 

 * Journ. of Arts and Science, 1881, vol. xxii. p. 90. 



