112 Dr. Hale on the Meteorological Journal 
wards. The mean difference, for these three years, between 
ten P. M. and sunrise, is 3,47°. I find by comparing a considera- 
ble number of my own observations, that the mean of the least 
heat in the twenty-four hours, as compared with that at sunrise, 
is 2,72° less than that ; making 6,19° as the difference between 
the mean temperature at ten P. M., and the probable mean of 
the greatest cold in each day. The true temperature indicated 
by these journals, corrected by these data, would stand as fol- 
lows. For the seven years published by Dr. Holyoke himself, 
the mean temperature at ten P. M.is 43,7°; from which deduct 
6,19°%, and it gives 37,51° as the mean of the greatest cold each 
day. The observation at noon, we have already remarked, is 
designed to give the greatest heat, the mean of which for the 
seven years is 54,15°, Taking these as the two extremes for each 
day, it gives 45,83° as the mean temperature of the seven years, 
from 1786 to-1792. For the whole period of thirty-six years, 
the mean by the four observations a day is 49,14°. By the cor- 
rection it will be as follows. The mean at ten P. M. 44,179, 
deduct 6,19°, leaves 38,53°; 56,05° is the mean of the observa- 
tions at noon; and the mean of the two is 47,29°, the estimated 
temperature by the whole series of observations. 
In September, 1818, Dr. Hoiyoke began a regular observa- 
tion, called in the journal, “ Night Thermometer,” which appears 
to have been kept by a self-registering thermometer, and to give 
the greatest cold of each day. This is continued in addition to 
the other observations already mentioned, to the end of 1821, 
the time when the journal communicated to the Academy termi- 
nates. On comparing the results of these observations with 
those made at ten P. M., I find the difference somewhat greater, 
than I have supposed it in the preceding calculation ; the mean 
