352 Br. blagden’s Hiflory of 
marking their fimultaneous defcents on a more extended fcale, 
or as long as both of them fhould continue to contract regu- 
larly. The fpecific gravity of the alcohol employed to make 
thefe thermometers was found to be 0,8254, in a temperature of 
^8°1 ; and they were graduated on the principle of two fixed 
points, one, the real freezing point of water fixed by aCtual 
experiment; the other, the i22d degree above o, determined 
by comparifon with a ftandard mercurial thermometer. This 
interval being divided into 90 parts, the degrees fo found were 
meafured downward as well as upward on the fcale, with a pro- 
per allowance for inequality in the bore of the tube. A fubfequent 
experiment fhewed that the freezing point had been rightly 
marked upon thefe inftruments ; but that, in confequence of a 
common fault in conftruCting thermometers, of not heating 
the contents of the tube fo much as thofe of the ball, the 
point of 122° was marked on both of them lower than it ought 
by the fpace of two degrees ; fo that 1 22° on the fcale indicated 
only 1 20 degrees above o of real heat. Any detail of the ob- 
fervations that were made to fettle the relative contractions of 
quickflver and fpirits by means of thefe inftruments would be 
improper at prefent ; it is fufficient to mention, that on one of 
them the 29th degree below o, and on the other the 30th, were 
found to correfpond with - 40° of the fmall mercurial ther- 
mometers, or more precifely with the point that would have 
been -3 9 0 upon an exaCt ftandard inftrument. 
The other objeCt for which the fpirit- thermometers were 
propofed, is more immediately connected with the congelation 
of mercury. All former experiments with frigorific mix- 
tures had left us abfolutely in the dark with regard to the de- 
gree of cold that was really produced. By thefe inftruments 
it is now determined, that the greateft cffcCt of a mixture of 
fnow. 
