C 422 ] 
12 gr. or 14.28 grains. All the pieces of my hy- 
grometer being put together, it weighed 373 grains, 
and when filled with the proper quantity of mercury 
833. It confequently contained 460 grains of 
mercury. 
46. By the rule above given (23), the extent of 
the hygrometer’s degrees, ought to be to that of the 
degrees in the preparatory thermometer, in propor- 
tion of the refpe&ive weights of mercury in the hy- 
grometer and thermometer ; and confequently as the 
weight of the mercury in the thermometer is to the 
weight of the mercury in the hygrometer, fo is any 
given interval in the thermometrical fcale, to the 
correfponding interval in the fcale of the hygro- 
meter. Confequently in our example as 1428 : 460 
:: 1937 : 624 (nearly) ; and the correfponding in- 
tervals on the fcales of the thermometer and the hy- 
grometer, ought to follow the proportion of 1937 
to 624. 
47. I call the diftance between the two fixed 
points of heat in the thermometer the fundamental 
interval ; and 1 fhall call the fundamental line in 
the hygrometer that of which the length corre- 
fponds to this interval. Thus the fundamental in- 
terval in the preparatory thermometer, being j 93 7 
parts of a certain fcale, the fundamental line of my 
hygrometer confiffed of 624 parts of the fame 
fcale. This example may fo eafily be applied, that 
it will be unneceffary to dwell any longer upon this 
fubjeft. 
48. Having thus got a fundamental line in the 
hygrometer, I had it in my power to divide it into 
as many parts as I thought proper : my choice was 
naturally 
