744 COMMEMORATION OB^ PROF. HENRY A. ROWLAND. 



ford, and finished by Rowland nearly a hundred years later. In prin- 

 ciple the method of Rowland was essentiall}^ that of Rumf ord. 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. 

 Rumford 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. Rowland 

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

 and diffusion of knowledge, aided by all the resources and refinements 

 in measurement which a hundred years of exact science had made pos- 

 sible. As the mechanical theory of heat was the germ out of which 

 grew the principle of the conservation of energy, an exact determina- 

 tion 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 j^ears. He employed various methods, finally 

 recurring to the early method of heating water by friction, improving 

 on Rumford's device by creating friction in the water itself. Joule's 

 last experiments were made in 1878, and most of Rowland's work was 

 done in the year following. It excelled that of Joule, not only in the 

 magnitude of the quantities to be observed, but especiall}?^ in the greater 

 attention given to the matter of thermometry. In conmion with Joule 

 and other previous investigators, he made use of mercury thermome- 

 ters, but this was only for convenience, and they were constantly com- 

 pared with an air thermometer, the results being fintdly reduced to the 

 absolute scale. B}^ experimenting with water at different initial tem- 

 peratures he obtained slightly different values for the mechanical 

 equivalent of heat, thus establishing beyond question the variability 

 of the specific heat of water. Indeed, so carefully and accurately was 

 the experiment worked out that he was able to draw the variation 

 curve and to show the existence of a minimum v^alue at 30° C. 



This elaborate and painstaking research, which is now classical, was 

 ever3'where awarded high praise. It was published in full by the 

 American Academy of Arts and Sciences with the aid of a fund origf- 

 nally established by Count Rumford, and in 1881 it was crowned as a 

 prize essay by the Venetian Institute. Its conclusions have stood the 

 test of twenty years of comparison and criticism. 



In the meantime Rowland's interest had been drawn, largely per- 

 haps through his association with his then colleague. Professor Hast- 

 ings, toward the stud}' of light. He was an early and able exponent 

 of Maxwell's magnetic theor}^ and he published important theoretical 

 discussions of electro-magnetic action. Recognizing the paramount 

 importance of the spectrum as a key to the solution of problems in 



