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it with December, 1873, we find in some respects the converse of 
the last instance. The mean height of the barometer in 1872 was 
lower by seven-tenths of an inch than in 1873, but the mean 
temperatures of the air and dew-point were nearly the same, and 
the mean humidity absolutely the same in both months. Yet 
while the rain-fall in December, 1872, amounted to 4.825 in., 
that of December, 1873, was only 0.564 inches, or more than eight 
times less. These results seem to point to the higher strata of the 
air,—above the action of the instruments, barometer excepted,—as 
the source of the increased condensation in 1872. 
A few examples may be taken from the summer months. Thus 
June 1868 and June 1869 are remarkable for having had the 
mean height of the barometer very nearly the same (only a 
difference of seven-hundredths of an inch), and the mean dew-point 
absolutely the same, in both months. But a great difference 
occurs in the mean humidity and in the rain-fall. In June, 1868, 
the mean humidity is only 72, and the rain-fall little more than 
half an inch. In June, 1869, the mean humidity is 81, and the 
rain-fall nearly an inch and a half. This difference is quite 
explained when we look to the mean temperature of the air in the 
two months, that of June, 1868, being nearly five degrees higher 
than in June, 1869; and it shows that the general temperature 
must be taken into account, as well as the barometer and dew- 
point, when inquiring into the causes of rain and humidity. 
Comparing again June 1872 with June 1873,—hetween which 
months there is not much difference either in the mean height of 
the barometer, or in the mean temperature of the air, or in the 
mean depression of the dew-point below the temperature of the 
air,—we find the rain-fall of June, 1872, more than three times 
that of June, 1873. It is also observable that the mean relative 
humidity of the former month was 82 while the mean relative 
humidity of the latter was 86, so that the month with the less 
quantity of rain was much more humid than the month with. the 
larger quantity of rain. This, however, is but an instance of 
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