Comparison of Thermometers. 91 



Equivalent as given by Joule in terms of water 



at 6o° F. and the latitude of Greenwich... 772*55 



Reduced to Chappuis' nitrogen thermometer... 77465 



„ „ hydrogen thermometer.. 774*94 



Rowland, who has contributed much to the improvement 

 of the science of thermometry, and who is also the author 

 of a very important determination of the equivalent of heat 

 has reduced all his measurements to an air thermometer of 

 his own construction. Having sent one of his thermometers 

 to Dr. Joule, a comparison was made by the latter, which 

 brings Joule's scale into common relation with Rowland's 

 air thermometer. We possess no information as to how the 

 comparison was made, but, accepting it as correct, it would 

 be allowable to draw the conclusion that Rowland's equiva- 

 lent, if referred to M. Chappuis' nitrogen thermometer, 

 should be reduced by about one unit, so that at 15 C. it 

 would have a value of about 777*3 as against 775 found by 

 Joule. 



