438 Professor Tyndall [May 3, 10, and 17, 



man who in opposition to the scientific belief of his time could 

 experiment, and reason upon experiment, as did Eumford in the 

 investigation here referred to, cannot be lightly passed over.' " In 

 my opinion, the most dignified and impressive way of dealing with 

 labours like those of Eumford, is to show by simple quotations, well 

 selected, what their merits are. This I did in the book referred to 

 by Dr. Ellis, which was published at least eight years in advance of 

 his. But the expression of my admiration for Eumford was not 

 confined to the passage above quoted, which is taken from the 

 appendix to one of my lectures. In that lecture I drew attention to 

 Eumford's labours in the following words: — "I have particular 

 pleasure in directing the reader's attention to an abstract of Count 

 Eumford's memoir on the generation of heat by friction, contained 

 in the appendix to this lecture. Eumford in this memoir anni- 

 hilates the material theory of heat. Nothing more powerful on the 

 subject has since been written." 



But I must not go too far, nor sufier myself to deal with one- 

 sided exclusivencss with the merits of Eumford. The theoretic 

 conceptions with which he dealt were not his conceptions, but had 

 been the property of science long prior to his day. This, I fear, was 

 forgotten when the following claim for Eumford was made by a 

 writer who has done excellent service in diffusing sound science 

 among the people of the United States : — " He was the man who first 

 took the question of the nature of heat out of the domain of meta- 

 physics, where it had been speculated upon since the time of Aristotle, 

 and placed it upon the true basis of physical experiment." The 

 writer of this passage could hardly, when he wrote it, have been 

 acquainted with the experiments and the reasonings of Boyle and 

 Hooke, and Leibnitz and Locke. As regards the nature of heat, 

 these men were quite as far removed from metaphysical subtleties 

 as Eumford himself. They regarded heat as " a very brisk agitation 

 of the insensible parts of an object which produces in us that sensa- 

 tion from whence we denominate the object hot ; so what in our 

 sensation is heat, in the object is nothing but motion." Locke, from 

 whom I here quote, and who merely expresses the ideas previously 

 enunciated by Boyle and Hooke, gives his reasons for holding this 

 theoretic conception. " This," he says, " appears by the way heat is 

 produced, for we see that the rubbing of a brass nail upon a board 

 will make it very hot ; and the axle-trees of carts and coaches are 

 often hot, and sometimes to a degree that it sets them on fire, by the 

 rubbing of the naves of the wheels upon them. On the other side, 

 the utmost degree of cold is the cessation of that motion of the 

 insensible particles which to our touch is heat." The precision of 

 this statement could not, within its limits, be exceeded at the present 

 day. 



There is a curious resemblance, moreover, between one of the 

 experiments of Boyle, and the most celebrated experiment of Eumford. 

 Boyle employed three men accustomed to the work, to hammer nimbly 



