Dkcbmbeb 6, 1901.] 



SCIENCE. 



869 



physical constant, which he determined 

 should be exhaustive in character and, for 

 some time to come at least, defiuitive. 

 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 impor- 

 tant. 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 experi- 

 ment was one surrounded by difficulties so 

 many and so great that few possessed the 

 courage to undertake it with the deliberate 

 expectation of greatly excelling anything 

 before accomplished. These things made it 

 attractive to Rowland. 



The overthrow of the materialistic theory 

 of heat, accompanied as it was by the ex- 

 perimental 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 number 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 Ameri- 

 can, Count Rumford, and finished by Row- 

 land, nearly a hundred years later. In 

 principle the method of Rowland was 

 essentially that of Rumford. 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 

 possible. 



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 princi- 

 ple, 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, im- 

 proving on Rumford's device by creating 

 friction in the water itself. Joule's last ex- 

 periments were made in 1878, and most of 

 Rowland's work was done in the year fol- 

 lowing. It excelled that of Joule, not only 

 in the magnitude of the quantities to be 

 observed, but especially in the greater at- 

 tention given to the matter of thermometry. 

 In common with Joule and other previous 

 investigators, he made use of mercury ther- 

 mometers, but this was only for convenience, 

 and they were constantly compared with an 

 air thermometer, the results being finally 

 reduced to the absolute scale. By experi- 

 menting 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 value at 30 de- 

 grees C. 



This elaborate and painstaking research, 

 which is now classical, was everywhere 

 awarded high praise. It was published in 

 full by the American Academy of Arts and 



