Address to the Royal Geological Society. 7 
restriction and limitation is often a positive, and not a mere 
negative boon; it is often a partial guidance towards the goal of 
truth. Our present object is by no means to escape from whole- 
some restriction, but only to relax the intolerable constriction to 
which the physicists, in their over-zeal for our welfare, would 
subject us. 
Sir W. Thomson’s argument was first drawn out in full in a 
paper communicated to the Geological Society of Glasgow, in 
1868 ; but it had been already partly put forth in former papers, 
as in that on the Secular Cooling of the Earth (Trans. Roy. Soc. 
Edinb. 1862), and in others. 
Professor Huxley replied in his Presidential Address to the 
Geological Society of London in 1869, but apparently without 
effect, for we find Professor Tait repeating the arguments, with 
his own modifications, in some lectures delivered in Edinburgh in 
1874. These lectures were published in the early part of 1876, 
and in the latter part of the same year Sir William himself 
repeated one of them in his Address to the Mathematical and 
Physical Section of the British Association, at Glasgow. 
We shall not now bring up any of Professor Huxley’s arguments 
in reply excepting one.* Of course in the following observations, 
as far as they are correct, we shall be only reminding our 
opponents of matters which they know better than we do, but 
which they have overlooked, while fixing their attention so 
strongly upon their own side of the question. 
Let us, then, take their three arguments as they are presented 
to us again by Professor Tait,t since Professor Huxley’s reply. 
The first is drawn from the rate of the earth’s secular cooling ; 
the second from the figure of the earth considered in connection 
with its present rate of rotation, as retarded by the action of the 
tides ; the third from the comparatively short time that the sun 
can be imagined to have kept, by its radiation, the earth’s surface 
in a state fit for the support of animal and vegetable life. 
A.—In our consideration of these arguments, it will be more 
suitable to invert their order, and to begin with the last men- 
tioned, viz., that drawn from the length of time that the sun 
can be imagined to have kept the earth, by its radiation, in a 
*;See his Pres. Address in Quart. Journ. Geol. Soc., Lond., vol. xxy., 1869. 
t Recent Advances in Physical Science, pp. 165 e¢ seg. 
