Ste i ee ie 
1871. ] Proceedings of the Asiatic Society. 161 
force describes equal spaces; for no person has an innate per- 
ception of equal times. Nobody can from his inner consciousness 
say one time is equal to another. Hours and minutes are as arbi- 
trary in their conception, and require just as much explanation 
as degrees of temperature. By general consent the earth is the 
standard body that has been selected to determine equal times 
by its motion, so that according to Newton’s law those times 
are called equal during which the earth describes equal spaces, 
or better during which any particular meridional plane describes 
equal angles. In fact when a person speaks of minutes or 
hours, he is tacidly assuming the fact of the earth’s inertia. 
And for comparing time without the aid of the earth’s rotation, 
clocks are used in which the condition of a body in motion, prac- 
tically unacted upon by any force, is arrived at by compensating 
by the action of a compressed spring or otherwise for the inevi- 
table forces of friction. 
The earth and moon regarded as a mechanical system possess 
a certain amount of “energy,” or power to do work. This energy 
is partly potential, that is, energy depending on the relative 
position of the earth and moon, and partly kinetic, that is, energy 
depending on the two bodies being in motion. Now the earth’s 
daily rotation produces tides by the mutual attraction of the sea 
and moon, and as the motion of the sea on the surface of the earth 
is retarded by tidal friction a certain amount of the energy pos- 
sessed by the system must be lost in overcoming the friction or in 
generating heat. 
One effect of this loss of energy is to cause the periods of rota- 
tion of the earth round its axis and of the moon round the earth 
to become more and more equal, or in other words to make the 
period of the earth’s diurnal rotation gradually longer and longer. 
The earth is, therefore, not a true time-keeper, and if a chrono- 
meter were set now to keep true sideral time, we should ex- 
pect, if the chronometer neither gained nor lost, to find at the 
end of a lapse of years, that it was apparently too fast, if com- 
pared with the then true sideral time. Such a chronometer it 
has been calculated would at the end of a century be apparently 
0°44 of a minute too fast. 
