ON TllE Afi-SOLUTK EXPANSION OF MERCURY. 2l 



(see l>elo\v, p. 22) was considered sufficient to show that no systematic change had 

 occurred in the working of the apparatus. 



In order to be able to reduce the olraervations with certainty to C., and to 

 obtain a direct value for the fundamental interval without extrapolation, it was 

 necessary to take a series of observations with the cold column at a temperature as 

 .near C. as possible. This point has already been explained in a previous section. 

 'By surrounding one side of the iron rectangle containing the cold column with a 

 jacket of melting ice, it was found possible to reduce the temperature to between 

 2 C. and 2'5 C. By further cooling the cold column to 10 C. with a freezing 

 mixture of ice and salt, while the hot column remained at the atmospheric tempe- 

 rature of 16 C., it was possible to obtain a good approximation to the coefficient at 

 C. These observations entailed much greater difficulty in manipulation than the 

 two previous series, but were valuable as giving direct evidence with regard to the 

 expansion la-tween 10 C. and +20 C. 



Series III. Observation* from -10 C. to 100 C. 



