366 HENRY A. ROWLAND 



reasonable to suppose that the glass was from the same source as the 

 standards Nos. 4 and 14 there used. We also know that Regnault was 

 consulted as to the methods, and that the apparatus for calibration 

 was obtained under his direction. 



I reproduce the table on preceding page with some alterations, the 

 principal one of which is the correction of the Troughton and Simms 

 thermometers, so as to read correctly at 32 and 212, the calibration 

 being assumed correct, but the divisions arbitrary. 



It is seen that the Kew standards and the Fastre agree perfectly, but 

 that the Troughton and Simms standard stands above the Kew ther- 

 mometers at 100 F. 



The Geissler standard was made by Geissler of Bonn, and its scale 

 was on a piece of milk glass, enclosed in a tube with the stem. The 

 calibration was fair, the greatest error being about 0-015 C., at 50 C.; 

 but no correction for calibration was made, as the instrument was only 

 used as a check for the other thermometers. 



3. EESULTS OF COMPARISON 

 Calculation of Air Thermometw 



This has already been described, and it only remains to discuss the 

 formula and constants, and the accuracy with which the different, 

 quantities must be known. 



The well-known formula for the air thermometer is 



ff-ft+4 



m _J 



* V 



i 



- fl 



V\ 'l + a? "1 + 0* J 



Solving with reference 1 to T, and placing in a more convenient form, 

 we have 



H-h' + *H-., 



T= - - _ nearlv, 



a A' _L_ __*_ 

 v 



where ' 



and r = a = -00364. 



For the first bulb, v 



For the second bulb, v_ 



V 



