Meteorological Observations. 673 
The mean monthly vapour point may also be 
inferred from the monthly evaporation and mean 
monthly temperature, according to the theory in 
the Essay, page 574.—Let August be taken for 
an instance: the evaporation was 5,798 inches= 
1312 grains from my small gage, which is nearly 
6 inches in diameter: but 1312 + 1440 (= min. 
in 24 hours) =.91 gr. per minute, the mean 
rate of evaporation, The mean temperature 
(taken from the mean noon and evening obser- 
vations) was 63°, with which entering table at 
page 587, we obtain 3. 63 grains, the evaporat- 
ing force at that temperature (taken from the 
third column, because the evaporating gage is in 
a very open situation). Subtracting .g1, there 
remains 2. 72 grains, corresponding in the said 
table to 54° 3, the mean vapour point. The 
mean derived from actual observation is stated 
above to be 541°. 
o 
AUROR® BOREALESS? 
Observed since 1793*. 
1794. January, 7and 22. March, 8 and 29, 
December, 8 and 1g. —Total, 6. 
1795. September, 8 and 14.—Total, 2. 
1796. None observed. 
* For those observed by me preceding that lee see 
my Meteorol. Obs. page 54. 
