192 Mr. Wollaston's description of the 
variation of 395 parts, or 1,643 i n °h on thermometrical baro- 
meter. My whole scale of 1000 parts would therefore equal 
2,52 of barometer, and comprehend all changes from 28,1 to 
30.6, if wanted to compare its variations with those of a com- 
mon barometer. Having observed also with a former ther- 
mometer mounted on this scale, that i° Fahrenheit or 0,589 
barometer, was equal to an elevation of about 530 feet, I 
reckon that as on my thermometrical barometer 500 parts 
from the top would correspond with 29,3 barometer, I have 
at any height from 29,3 upwards, the other 500 parts or more 
to be applied to the measurement of altitudes, which allow- 
ing 233 parts to 530 feet, will comprehend every thing that 
can be wanted in this part of the kingdom. This being 
convenient for all my purposes, the thermometer was to be 
set to this point. I therefore first drew all the mercury from 
the cap F into the tube, and then expanding it carefully and 
gradually out, shook off the globules at top, till it should 
stand on boiling at such height according to the state of the 
barometer at the time, that by computation the top and 
bottom of the scale should correspond with 30,6 and 28,1 
respectively. It is for the shaking off this globule that the 
fine tube must be broken abruptly at top and end flat ; and 
there is no fear of the globule being drawn down again into 
the tube, unless the whole column is expanded to the top and 
connected with the globule in F. 
Yet this instrument, though adjusted now to my own par- 
ticular use by the quantity of mercury in the thread, is capa- 
ble of measuring any greater altitude, even Mt. Blanc or 
Chimborazo, under any barometrical circumstances, and the 
change for that purpose is much easier effected than would 
