1G Dr. 1). F. Comstock on the 
as it moved through space, and it might be possible to 
account in this way for some of the energy which is ordinarily 
thought of as totally dissipated. 
Another conclusion which is suggested by the foregoing is 
that, assuming the loss of: mass accompanying dissipation of 
energy, the sun's mass must have decreased steadily throuoh 
millions of years. If too, our conclusion respecting the 
gravitating quality of confined energy be correct, the gravita- 
tion constant of the sun has also decreased and the distances 
of the planets must have increased accordingly. This last 
increase of planetary distance can be calculated by making 
the angular momentum of the planet about the sun a 
constant, and allowing the mass of the planet, together 
with the gravities of both sun and planet, to grow less with 
time. 
80 little is known as to the former radiating power of the 
sun that no even approximate calculation can be made, but 
it is not difficult to show that the order of magnitude is such 
as might make the increase in the planetary distances not 
altogether negligible during great lapses of time. 
A P roof from a different Point of View. 
16. The proof of expression (17) which has been given has 
the advantage of entering intimately into the structure of 
the general system and showing the part that non-electrical 
forces in the form of constraints must play if the fundamental 
laws of electrical action are to hold for every infinitesimal 
element of the finite volume occupied by any electrical 
system. Although this is assumed in every mathematical 
derivation of the mass of an electron, and in fact in all 
problems of a similar nature, many will doubtless object to 
this assumption on the ground that probably the ordinary 
electrical laws do not apply when the distance between 
" elements of charge," so called, is comparable with the 
diameter of an electron. 
Although it is difficult to see how a coherent mathematical 
theory of electricity can at present be formed without this 
assumption, yet it was thought best to add a more general 
proof of (17). The following is therefore given as avoiding 
the explicit use of constraints. 
17. The statement of the law of the conservation of energy 
for an element of volume in any electrical system possessing 
electrical charges in motion, is the well-known expression 
5r=-tar + ^ + 3r)- *A+w* f .+«vA) ' ' ' 
