COMMEMORATION OF 1»R<)F. HENRY A. ROWLAND. 74.". 



tional evidence in corroboration of his views, in the fall of the year 

 1900 the problem was again attacked in hisown laboratory, and he had 

 the satisfaction, only a short time before his death, of seeing a com- 

 plete confirmation of the results lie had announced a quarter of a 

 century earlier, concerning which, however, there had never been the 

 slightest doubt in hisown mind. It is a further satisfaction to his 

 friends to know that a very recent investigation at the Jefferson 

 Physical Laboratory of Harvard University, in which Rowland's meth- 

 ods were modified so as to meet etf'ecti ely the objections made by his 

 critics, has resulted in a complete verification of his conclusions. 



On his return from Europe, in 1876, his time was much occupied 

 with the beginning of the active duties of his professorship, and espe- 

 cially in putting in order the equipment of the laboratory over which 

 he was to preside, much of which he had ordered while in Europe. In 

 its arrangement a great many of his friends thought undue prominence 

 was given to the workshop, its machinery, tools, and especially the 

 men who were to be employed in it. He planned wisely, however, for 

 he meant to see to it that much, perhaps most, of the work under his 

 direction should be in the nature of original investigation, for the suc- 

 cessful execution of which a well-manned and equipped workshop is 

 worth more than a storehouse of apparatus already designed and used 

 by others. 



He shortly found leisure, however, to plan an elaborate research 

 upon the mechanical equivalent of heat, and to design and supervise 

 the construction of the necessary apparatus for a determination of the 

 numerical value of this most important physical constant, which he 

 determined should be exhaustive in character and, for some time to 

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

 originality and boldness of inception by which man}- 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 excel- 

 ling anything before accomplished. These things made it attractive to 

 Rowland. 



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 1 pound of water 1 in tempera- 

 ture, has, with much reason, been called the golden number of that 

 century. Its determination was begun by an American, Count Rum- 



