464 Molecules, Ultimates, Atom$, and Waves. [October, 



The amount of this pressure is equivalent to that of 30 

 inches of mercury, corresponding to 4,809,528 inches of 

 hydrogen of uniform density. Thus, in order to maintain 

 the ultimates of hydrogen contained in a length of a million 

 inches, in that degree of mutual proximity which enables 

 them to exert on the wave-motion of light a retarding force 

 equivalent to that which would be exerted by only 138 

 inches of the free ether, requires the gravitating force of 

 nearly five times that quantity of hydrogen. The force 

 which balances this pressure can be nothing but the repul- 

 sion of the particles of the ether for the ultimates of hydro- 

 gen. In the length of a million inches, the same number 

 of ethereal particles exist in the absence of the hydrogen, 

 as in its presence, the hydrogen ultimates insinuating 

 themselves between the particles of the ether. Their doing 

 so is facilitated by the extreme minuteness of the probable 

 diameter of the ethereal particles, in comparison with the 

 size of the intervals between them. Of the ratio which the 

 former bears to the latter, a fair estimate may be formed 

 from the proportion which the departure of the particles 

 from their points of rest, in the case of the shortest wave, 

 bears to what it is in the case of the longest wave — this 

 proportion being as 1 to 42,000. The effect produced by the 

 hydrogen is the same as would follow the introduction of an 

 additional quantity of 138 inches into the million inches of 

 the ether — equivalent to an addition of 1-7246^ part of 

 the number of ethereal particles embraced in the latter 

 space, or to a corresponding diminution in the length of the 

 intervals between them. 



Were the ultimates of hydrogen homogeneous simple 

 masses, they might be supposed to be interspersed along the 

 line of ethereal particles at comparatively considerable 

 intervals ; while the ethereal particles intervening between 

 each pair of hydrogenous ultimates might be supposed 

 to be forced into greater mutual proximity — so having 

 their mutual distances diminished by 1-7246^ part. But 

 according to this view, the compressing force could 

 be only the mutual gravitation of the hydrogenous 

 ultimates and their general gravitation towards the 

 earth, aided by the superincumbent pressure. When 

 it is borne in mind, however, that the mutually repellent 

 force of the ethereal particles is more than a billion 

 of times greater than the force of terrestrial gravitation 

 as it subsists in the lower strata of the atmosphere, it 

 will be perceived how inadequate the latter is to produce the 

 observed amount of compression, and that some other 



