282 ON LIGHT. 



the inertia of its molecules, to give rise to an equally rapid 

 transmission of a wave through it. For it results from 

 the theory of sound that in media of different elasticities 

 (so understood), but similarly constituted in other re- 

 spects, these forces are to each other as the squares of 

 the velocities with which the waves travel : so that the 

 elastic force of the air would require to be increased in 

 the proportion of the square of 901,000 (i.e., 811,801 

 millions) to i, to produce an equal velocity. Even this 

 enormous number must be still further increased, since 

 the velocity of sound is augmented by a peculiarity in 

 the constitution of air which we should hardly be justified 

 in attributing to the luminiferous ether, in virtue of 

 which its elasticity is increased by heat given out in the 

 act of its compression, and without which the velocity of 

 sound would be only 916 feet per second instead of 

 1090. Thus the number above arrived at has to be 

 further increased in the proportion of the square of 1090 

 to that of 916, which brings it to 1,148,000,000,000. 

 Let us suppose now that an amount of our etherial 

 medium equal in quantity of matter to that which is con- 

 tained in a cubic inch of air (which weighs about one- 

 third of a grain) were enclosed in a cube of an inch in the 

 side. The bursting power of air so enclosed we know to- 

 be 15 Ibs. on each side of the cube. That of the impri- 

 soned ether then would be 15 times the above immense 

 number (or upwards of 17 billions) of pounds. Do what 

 we will adopt what hypotheses we please there is no 

 escape, in dealing with the phenomena of light, from 

 these gigantic numbers ; or irom the conception of enor 



