302 PROCEEDINGS OF THE AMERICAN ACADEMY. 



It may be asked whether the method of investigation which has 

 been described at such length in this paper will be applicable to the 

 case of metals in general, and whether it can be extended through 

 any large range of temperature. It is evident that the thermo-electric 

 device for determining the difference of temperature between the two 

 faces of the disk must be used with great caution, and will in some 

 cases be difficult of operation ; but its use is by no means restricted to 

 iron. Copper and other metals thermo-electrically near it will cer- 

 tainly give some trouble, though it is believed that they can be suc- 

 cessfully dealt with. It is probable that the range of temperature 

 can be greatly increased by the use of other liquids instead of water ; 

 but if this is done, the question as to the specific heat of the liquid 

 will become a difficult one. 



The method described is a laborious one in its preparatory stages, 

 but much of the initial work can be done by a mechanic. The opera- 

 tion of the apparatus, once prepared, is comparatively easy, and the 

 calculations are simple. A single experimenter operates the whole 

 machinery, and makes all the observations. He can make the A and £ 

 observations for a given temperature and calculate the value of k 

 therefrom in one day, without excessive toil, and with a reasonable 

 assurance that the result will be in accord with that of the day 

 before. 



This investigation was begun, at the author's suggestion, some years 

 ago by IMr. A. W.'Slocum, then a graduate student at Harvard, now 

 of the University of Vermont. Mr. Slocum worked with great zeal 

 and energy, and made substantial progress, but presently went abroad, 

 leaving the research in my hands. 



I have to thank all members of the Physical Department at Har- 

 vard, who have given me extremely valuable suggestions in regard to 

 my work, and have furthered it by every means in their power. 



