22 Prof. Maxwell on the Theory of Molecular Vortices 



Prop. XVI. — To find the rate of propagation of transverse 

 vibrations through the clastic medium of which the cells are 

 composed, on the supposition that its elasticity is due entirely to 

 forces acting between pairs of particles. 



By the ordinary method of investigation we know that 



= ^/- * (132) 



V: 



P 



where m is the coefficient of transverse elasticity, and p is the 

 density. By referring to the equations of Part I., it will be seen 

 that if p is the density of the matter of the vortices, and pu is the 

 " coefficient of magnetic induction/ 5 



pL = 7rp; ....... (133) 



whence 



7rm=V 2 /z; ...... (134) 



and by (108), 



E=V*//a (135) 



In air or vacuum ft=l, and therefore 

 V=E, 

 = 310,740,000,000 millimetres per second I . (136) 

 = 193,088 miles per second. 



The velocity of light in air, as determined by M. Pizeau*, is 

 70,843 leagues per second (25 leagues to a degree) which gives 



V= 314,858,000,000 millimetres 

 = 195,647 miles per second (137) 



The velocity of transverse undulations in our hypothetical medium, 

 calculated from the electro-magnetic experiments of MM. Kohl- 

 rausch and Weber, agrees so exactly with the velocity of light 

 calculated from the optical experiments of M. Pizeau, that we 

 can scarcely avoid the inference that light consists in the transverse 

 undulations of the same medium which is the cause of electric and 

 magnetic phenomena. 



Prop, XVII. — To find the electric capacity of a Leyden jar 

 composed of any given dielectric placed between two conducting 

 surfaces. 



Let the electric tensions or potentials of the two surfaces be M/*, 

 and ^Pq. Let S be the area of each surface, and the distance 

 between them, and let e and — e be the quantities of electricity 



* Comptes Rendus, vol. xxix. (1849), p. 90. In Galbraith and Haugh- 

 ton's 'Manual of Astronomy/ M. Fizeau's result is stated at 169,944 geo- 

 graphical miles of 1000 fathoms, which gives 193,118 statute miles; the 

 value deduced from aberration is 192,000 miles. 



