378 HENRY A. BOWLAND 



Hence for 6163 we have in this way 



C = -057381 C" = -056995 m = -000187. 



By direct comparison of No. 6163 with the air thermometer., we find 

 the following: 



m. 



000239 

 000166 

 000226 

 000155 

 000071 

 .000115 



Mean -056976 -000004 -000154 -000010 



The values of C" agree with each other with great exactness, and 

 the probable error is only 0-003 C. at the 40 point. 



The great differences in the values of m, when we estimate exactly 

 what they mean in degrees, also show great exactness in the experi- 

 ments. The mean value of m indicates a difference of only 0-05 

 between the mercurial and air thermometer at the 20 point, the 

 and 40 points coinciding. The probable error of m in degrees is only 

 0.003C. 



There is one more method of finding m from these experiments; and 

 that is by comparing the values of C' with No. 6167, the glass of 6167 

 being supposed to be the same as that of 6163. 



We have the formula 



C = C"(l + 34-8??i). 



Hence 



CC' 



m = 



3i-SC' 



We thus obtain the following results: 



Mean -000213 



