Rowland's Thermometer* loith the Paris Standard. 27 



1879, Joule himself made a comparison of Rowland's thermo- 

 meter, Baudin 6166, with bis own thermometer, and the 

 results were published by Rowland (Proc. Am. Acad. vol. xvi. 

 p. 38, 1880-81). In 1892-94, Schuster made a comparison 

 of Joule's thermometer with a Tonnelot that had been 

 standardized at the International Bureau, and he reduced the 

 indications of the Joule thermometer to the Paris nitrogen 

 scale (Schuster, Phil. Mag. vol. xxxix. p. 477, 1895). These 

 two comparisons should give a means of reducing the 

 indications of Rowland's thermometer to the Paris nitrogen 

 or hydrogen scale. The present writer has made an 

 examination of the comparisons of Schuster and of Joule, 

 and, by means of a graphic method, the results obtained by 

 Schuster's indirect comparison were compared with those 

 obtained from the present series. The curves drawn are 

 shown in fig. 5. The notation used is intended to be 

 suggestive of the meaning of the curves. 



Fig. 5. 



The ordinates of the curve marked T RA — T Ab8 give the 

 difference between the air-thermometer and the absolute scale, 

 as used by Rowland. The ordinates of the curve T^ — T H 

 represent the difference between the nitrogen and the hydrooen 

 scale, according to Chappuis. The ordinates of the curve 

 T H — T Aba , which is not shown in fig. 5, represent the difference 

 between the hydrogen scale and Rowland's absolute scale 



