Comparisons of Mercury and Platinum Thermometers. 27 



circuited and all plugs replaced with care ; these corrections 

 are applied in column III. 



By the application of these corrections, taken with proper 

 signs, we get R, the resistance of the platinum thermometer, 

 shown in column V. 



The platinum temperature, shown in column VI., is de- 

 duced from the observed value of R by substitution in the 

 formula defining platinum temperature, remembering that 

 R = 258-471 and R 1 = 358"231 "mean box-units at 20° C." 



From the platinum temperature the corresponding tempe- 

 rature on the air-scale, shown in column VII., is deduced by 

 the formula 



,- P * = i-49i{(4) e -4}. 



In order to facilitate these reductions, a table was con- 

 structed giving the value of (t—pt) for every degree pt on 

 the platinum scale. 



Six determinations of the zero of Baudin 6166 gave the 

 following results : — 



mm. 

 24-159 

 24-147 

 24-151 

 24-148 

 24-151 

 24-154 



Mean . . 24*15 



Rowland's zero (table xx. p. 116, Proc. Amer. Acad, of 

 Arts and Sciences, xv. 1879) was 2043. 



Temperatures by Baudin 6166 are reduced as follows : — To 

 the mean stem-reading is applied the stem-correction which 

 is divided into two parts, one portion of the stem extending 

 from 28 mm. to 99 mm. being assumed to be at the tempe- 

 rature of the water in the surrounding jacket, the remainder 

 of the stem at the temperature of the surrounding air. This 

 correction is applied in column XI. ; from the corrected 

 stem-reading the corresponding temperature on Rowland's 

 air thermometer is obtained from the results of his comparisons 

 of these thermometers with the air thermometer given in 

 his tables xviii., xix., and xx. The temperatures thus ob- 

 tained must be further corrected by the rise of the zero since 

 Rowland's comparisons : this is shown in column XII., which 

 gives the mean temperature on the Rowland air-scale (obtained 

 through 6166), corresponding to the mean temperature on 

 the Callendar- Griffiths air-scale given in column VII. 



