.v/A' WILL/AM SIEAfENS, F.K.S. 183 



steam for propelling us both by land and sea at a speed rivalling 

 that of our friends the deer and the eagle, and for accomplishing 

 for us the innumerable purposes of grinding, spinning, pumping, 

 and lifting, upon which our material well-being now depends. 

 It would not be too much to say that the power of man consists 

 really in his ability to direct the forces of nature, and that the 

 degree of civilisation to which he has attained is commensurate 

 with his command of those forces. It is therefore no idle ques- 

 tion on which I intend to address you this evening, and I feel 

 much oppressed with the weight of matter which I have to bring 

 before you, although I shall not attempt to deal with more than a 

 few points, to which I hope to be able to attract your interest. 



In order to understand the forces of nature, and to direct their 

 application, it is necessary that we should at least have a general 

 conception of their origin. The time was not long ago when the 

 forces in nature appeared to us as spasmodic and unconnected, 

 when the energy of the wind and of the falling stream, the energy 

 displayed in vegetation and in muscular action, the force of heat 

 and the almost unknown force of electricity appeared to have no 

 connection with one another, and seemed to be beyond the reach 

 of human calculation. 



The probability of connecting-links between the different forces 

 of nature has, however, presented itself to some of the greatest 

 minds of different ages ; thus, Aristotle, " considered the first 

 principle in nature to be a unity of all its manifestations, and the 

 manifestations themselves he reduced always to motion as their 

 foundation." Again, in Lord Bacon's " Aphorisms," the chapter on 

 " The First Vintages of the Force of Heat " contains the follow- 

 ing remarkable passage : " From the instances taken collectively, 

 as well as singly, the nature whose limit is heat appears to be 

 motion." And further on, " But that the very essence of heat, or 

 the substantial self of heat, is motion, and nothing else limited," 

 &c. Bacon fails, however, in his attempts to prove his philo- 

 sophy, by confounding the visible motion of heating water, or of 

 fire, with the intrinsic motion of the particles that manifests 

 itself as heat. 



Count Rumford, in 1798, made the first important advance to 

 connect heat with mechanical force, supporting his theory by 

 means of experiments which were intended to determine the actual 



