200 Mr. Groombridge’s Observations 
79 ; and for the thermometer \Vithout, from 24 to 80. The 
difference of these extremes being divided by 8, will show 
the corrections for the former to every 6°, and for the latter 
to every 7 0 ; and assuming that the variations are in a reci- 
procal ratio to the degrees of the thermometer, I propose the 
following formula. Putting h for the degree of Fahrenheit’s 
thermometer, then 49 0 — h° x ,0024, when below the mean ; 
49 0 — h° x ,0023, when above the mean; will be the correction 
for the thermometer within ; and 45 0 — h° x ,0021, the cor- 
rection for the thermometer without. The Tables II. and III. 
show the near agreement of the observed and the equated 
factor, found as above. The barometer at its mean state may 
continue to be taken at 29,6 inches ; and the mean point of 
the thermometer without, will then be at 45 0 . The thermo- 
meter within, which has been assumed at 50° for the mean 
state, from observation, appears to be at 49 0 ; and supposing the 
barometer and thermometer to vary reciprocally, as the for- 
mer in inches and the latter in degrees, the mean point of 
each is in an inverse ratio to the other, and might be changed 
if thought expedient. Indeed it appears from the mean of 
more than 1000 observations of these circumpolar stars, at 
all seasons, that the mean state of the barometer is 29.85, 
and of the thermometer 52 0 ; yet, as the sum of the two cor- 
rections would still be the same, there cannot be occasion to 
alter the mean point of the former, especially as this might 
not be a general rule for every climate. It has very rarely 
happened, that I could make any observation, when the baro- 
meter has been below 29 inches, which causes the mean state 
to be so high as 29,85 ; but it may be otherwise in places, 
