6 HENRY A. EOWLAND 



come, at least, definitive. While this work lacked the elements of 

 originality and boldness of inception by which many of his principal 

 researches are characterized, it was none the less important. While 

 doing over again what others had done before him, he meant to do it, 

 and did' do it, on a scale and in a way not before attempted. It was one 

 of the great constants of nature, and, besides, the experiment was one 

 surrounded by difficulties so many and so great that few possessed the 

 courage to undertake it with the deliberate expectation of greatly ex- 

 celling anything before accomplished. These things made it attractive 

 to Eowland. 



The overthrow of the materialistic theory of heat, accompanied as 

 it was by the experimental proof of its real nature, namely, that it is 

 essentially molecular energy, laid the foundation for one of those two 

 great generalizations in science which will ever constitute the glory of 

 the nineteenth century. The mechanical equivalent of heat, the num- 

 ber of units of work necessary to raise one pound of water one degree 

 in temperature, has, with much reason, been called the Golden Number 

 of that century. Its determination was begun by an American, Count 

 Eumford, and finished by Rowland nearly a hundred years later. In 

 principle the method of Eowland was essentially that of Eumford. 

 The first determination was, as we now know, in error by nearly 40 

 per cent; the last is probably accurate within a small fraction of 1 per 

 cent. Eumford began the work in the ordnance foundry of the Elector 

 of Bavaria at Munich, converting mechanical energy into heat by means 

 of a blunt boring tool in a cannon surrounded by a definite quantity 

 of water, the rise in temperature of which could be measured. Eowland 

 finished it in an establishment founded for and dedicated to the in- 

 crease and diffusion of knowledge, aided by all the resources and refine- 

 ments in measurement which a hundred years of exact science had 

 made possible. As the mechanical theory of heat was the germ out 

 of which grew the principle of the conservation of energy, an exact 

 determination of the relation of work and heat was necessary to a 

 rigorous proof of that principle, and Joule, of Manchester, to whom 

 belongs more of the credit for this proof than to any other one man or, 

 perhaps, to all others put together, experimented on the mechanical 

 equivalent of heat for more than forty years. He employed various 

 methods, finally recurring to the early method of heating water by 

 friction, improving on Eumford's device by creating friction in the 

 water itself. Joule's last experiments were made in 1878, and most 

 of Eowland's work was done in the year following. It excelled that of 



