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XXXVII. Experimental Researches on the Conductive Powers of various Substances, 
with the application of the Results to the Problem of Terrestrial Temperature. 
By W. Hopkins, Esp, M,A., F.R.S., of St. Peter's College, Cambridge. 
Eeceived June 10,— Eead June 18, 1857. 
In presenting this memoir to the Society, I feel myself called upon to acknowledge the 
hberal aid which I have received from the Committee for the disposal of the Annual 
Government Grant for the Advancement of Science, in the prosecution of the experi- 
mental researches in which I have been engaged for a considerable time. The present 
paper contains an account of a part only of my experiments, Avith the application of the 
results of them to the problem of terrestrial temperature. An account of the remaining 
experiments will be reserved for a future paper. I am likewise bound to express in the 
strongest terms my obhgations to my friends Mr. Faiebaien and Mr. Joule. Without 
the aid of the former of these gentlemen I should have been unable even to commence 
the series of experiments which I have now nearly concluded ; and among the many 
ways in which this assistance has been so promptly rendered, I may mention his having 
constantly placed at my disposal the invaluable services of one of his principal work- 
men, WiLLiAii MAed, without whose untiring activity and mechanical resources, I should 
have utterly despaired of bringing my experiments to any successful issue. The value 
of Mr. Joule’s assistance, especially in the commencement of these experiments, will be 
understood by those who are acquainted with his sound philosophical knowledge and 
experimental skill. More specific acknowledgement of his services will be called for in 
my next communication. I now proceed to the subject of this paper. 
^ I. General Experimental Results respecting the Conductive Power of various Substances, 
and the circumstances by which it is affected, 
1. That I may be able to state the more clearly the nature of the quantity which 
measures the conducti\ity of any proposed substance with reference to heat, and the 
experimental method I have adopted for the determination of its value, it will be neces- 
sary to recall the solution of the problem, under one of its simplest aspects, the object 
of which is to ascertain the manner in which heat is transmitted by conduction through 
a body under certain conditions. Conceive the body to be bounded by two parallel 
plane surfaces of indefinite extent, the distance between them being h. Suppose one of 
these bounding sm’faces (which, for convenience, may be termed the lower one) to be 
kept at a uniform and constant temperature t^, while the temperature of the free space 
into which the heat radiates from the upper surface, is constant and =r. Also let ^ 
5 N 
MDCCCLVII. 
