meafuring Heights with the Barometer. 737 
rays : I apprehend that I have not exceeded, hut rather 
fallen fhort, in the reduction, to what would have been 
indicated by thermometers in the fhade, perfectly free 
from direft and reflected heat, and with fufficient time 
allowed between the obfervations. Be this as it may, it 
is of no importance, as no other conclufion is drawn 
from thefe obfervations, than that of Brewing what, in 
my apprehenfion, might probably have been the cafe, it 
another mode had been adopted. 
From the table it appears, that when the temperature 
of the air is at 29 0 . 5, the logarithmic excefs is ~o5 and 
at 7 5 0 . 5 reduced temperature, the defect is The 
-fum of the tw r o equations ™V being divided by the dif- 
ference of temperature 46°, we have, as in the Britifh 
obfervations, nearly 2.3 for each degree-, which is greater 
than that applied by Mr. de luc’s rule, in the proportion 
of 2 3 to 2 1 . That too fmall an equation hath been made 
ufe of in thefe hotteft obfervations, fuppofing the origi- 
nal zero and temperature to remain, is fufficiently evi- 
dent: for being divided by 42 0 the difference of 
temperature, we have, as before, 2.3 very nearly for the 
equation anfwering to each degree. 
Farther, if we confider the ratio of the weight of 
quickfilver to air, actually refulting from the obferva- 
tions themfelves, the fame kind of error (for I cannot fee 
5 B 2 lt 
