44 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
In order to arrive at a numerical result we have to find the value 
i; 
of at and of these two quantities only one 4 has been experi- 
mentally determined. 
However, remembering that on the undulatory theory of light a 
diminishes with the distance from the centre of radiation we are 
certainly safe in supposing that even in the region of space we are 
considering @ cannot possibly be greater than 2002. 
It is scarcely possible that the velocity of the ether-particles can 
exceed 233,626,000 miles per 1”, the stupendous rate necessitated by 
_ and multiplying the 
result by (5280)? we conclude that the mass of a cubic mile of ether 
this supposition. Substituting for 
13 
is not less than 4 cc) of a pound. Now a cubic mile of air (at 
0° 760mm) contains (10)! Ibs. Therefore air is not more than 
4(10)* times denser than the ether. 
Using this value for the density, a sphere whose radius is the 
same as that of Neptune’s orbit, or 276,000,000 would contain 
2(10)” Ibs. of ether or a sphere whose radius is 95,000,000 miles, 
the distance of the earth from the sun, would contain 4,400,000- 
tons. 
If we suppose, as reasoning from acoustical analogies there is con- 
siderable reason for doing, that a instead of being 200 times. 
greater than A is 5 times less,a cubic mile of ether would contain 
1 : ; 
(5) lbs., or a sphere of the same dimensions as the earth would 
contain about 6,500 lbs. 
After having made the above calculations, and in the course of a 
R 
vain search for further data as to the value of = we found that some 
years ago Sir W. Thomson had attempted a similar undertaking, 
and by means of a somewhat different method of investigation, had 
arrived at the conclusion that the probable density of the ether was. 
25 times less than that given above. 
Considering the uncertainty of the assumption as to the ratio 
between the amplitude and wave-length of the ethereal vibrations, 
the coincidence is satisfactorily close. 
Although, as has been pointed out, the quantity of energy in the: 
