366 Sir george shuckburgh on the Variation 
gree into ten; with, moreover, a lens of an inch focus; 
this apparatus being made moveable full by the hand, 
and more delicately by means of a micrometer fcrew, 
whofe head was divided into twenty-five divifions, each 
equal to the fortieth of a degree (for lb truly cylindrical 
was the tube, which had been with care exprefsly fe- 
ledted from a great quantity of glafs, that the divifions in 
the neighbourhood of the freezing point did not differ 
from thofe near the boiling point by fo much as ~th of 
a degree, and this variation appeared in other parts of 
the tube flridtly uniform, as was found by breaking the 
column of mercury); by means I fay of this appara- 
tus t was enabled to read off any height of the thermos- 
meter to within j^th of a degree. The veffel, in which 
the water was boiled, which was always fpring water, 
was a cylindrical tin pot,. 1 3 inches high and 4^ inches 
wide, with a top fomething refembling that defcribed in 
Mr. de luc’s work, contrived to carry off the fleam with- 
out incommoding the obferver, with a wafle pipe for the 
fuperfluous water in boiling, which might otherwife fall 
upon the fire and extinguifh it. The ball of the ther- 
mometer was immerfed to within af inches of the bot- 
tom of the veffel, and 1 inches below the furface of 
the w r ater, fo that as near as might be the whole column 
of mercury was expofed to the heat of boiling water, 
there 
