Jrom an Increase of Temperature. 361 
Fig. 3. 
always in the same position in the instrument. p is the square 
pin fitting into the socket, and moved by the screw G, Fig. 1. 
The upper part of the rod was kept in the proper position, by 
means of slender springs of wire, which pressed a small roller against 
the front of the case, so that the upper stud always stood at the 
same distance from the object-glass of the upper micrometer. This 
is shewn by Fig. 4, which is a section of the upper part of the 
double case of the full size. A is the upper end of the rod 
under experiment. R the roller pressing on the front of the 
double case. SS the space through which the steam passes. B 
the upper stud opposite to the window and upper micrometer M. 
CC the back spring, E one of the side springs. F the cover of the 
top, which is double ; and the space between the upper and un- 
der plate is stuffed with cotton. T the bulb of the upper ther- 
mometer.. V is the upper pipe, by which any vapour coming 
from the enclosed rod may escape, when it is wished to allow the 
