1871.] Proceedings of the Asiatic Society. 165 
the sea, than to show that a retardation of the earth does not exist 
or that the rate of this retardation could not be calculated. The 
calculation to which I have alluded of 0.44 of a minute and to which 
Colonel Tennant objects so strongly was obtained in the following 
way by Prof. Thomson, Mr. Adams and Prof. Tait working together. 
They started with the assumption that the known difference between 
the acceleration of the moon relative to the earth, as calculated by 
Mr. Adams, and the actual relative acceleration, as observed by 
Mr. Dunthorne, was due to tidal friction, and then by allowing for 
the necessary consequent retardation of the moon’s mean motion, 
and using a certain assumption with regard to the proportion of 
the retardations due to the moon and sun, they arrived at the 
result I have given. Now with reference to the general question, 
independently of any calculation, it appears to me that as long 
as the sea moves on the surface of the earth there must be 
tidal friction: Friction must produce heat. Heat produced in any 
system of bodies must to a certain extent be dissipated unless 
the heated bodies be surrounded by a perfectly non-conducting 
thermal envelope, a thing of course quite unknown. Wherever, 
therefore, heat is produced, there must be a certain loss of energy. 
And the loss of energy in the case in question must cause a retar- 
dation in the earth’s diurnal rotation, unless there exists some 
other cause not yet ascertained which compensates for this loss of 
energy. ‘The connection, therefore, between tidal friction and the 
undoubted fact of the earth’s retardation possesses, I think, a high 
degree of probability. 
The President understood Mr. Ayrton’s remarks on Inertia to 
be intended to lead up to the principal topic of his short paper. 
Mr. Adams demonstrated, now many years ago, that Laplace’s 
celebrated explanation of the Moon’s acceleration was not nearly 
so complete as it had been thought to be, It left about one half 
of the inequality unaccounted for. But, to discover the true cause 
of this residuum was a task of the greatest difficulty. Any one 
who had practical experience in dealing with the formule of the 
Lunar Theory would know quite well how complicated the problem 
was. The best supposition—one he believed that was at this time 
