44. 
quency of rain had been ascertained. In 1870 and 1871 rain fell most 
frequently from two to three in the afternoon, and least frequently 
from 11 p.m. to midnight. Mr. Glaisher had previously found that at 
Greenwich the period of maximum frequency was from two to three 
p.m., and observations made in Philadelphia also gave the same results. 
The frequency of rain in the early afternoon hours was probably 
occasioned by a condensation of vapour when the sun was beginning to 
descend, and when a diminution in its heating power had taken place ; 
a second maximum period occurred about the time of sun-rising, when 
the temperature was usually at its minimum. Secondly, the total dura- 
tion of rain was 593 hours in 1870, and 538 hours in 1871, in both of 
which years the rainfall was below the average, so he thought it might 
fairly be assumed that in an average year rain fell for one month out of 
it. Thirdly, by dividing the total rainfall by the duration, the rate had 
been calculated. He was not aware that the rate of rainfall had ever 
been calculated for any length of time, and the results were therefore 
of special interest. In 1870 he found that the rate in the summer was 
exactly double that of the winter, while that of the autumn was within a 
fraction double that of the spring ; or, to put it more plainly, that rain 
falls twice as fast in the summer as in the winter, and twice as fast in 
the autumn as in the spring. In 1871 the first part of this rule was 
again verified, but, owing to the autumn drought, the rate then was 
not different from that of the spring. 
The necessity fcr correct knowledge as to rainfall, which was re- 
quired both for water companies and for drainage and other engineer- 
ing works, had induced many persons to record the amount which fell, 
for which purpose several different forms of rain gauges had been de- 
signed, but observers had generally returned to the simple form used 
by Luke Howard, ‘‘ The Father of English Meteorology.” 
The earliest English rainfall observer was Mr. Townley, of Townley, 
in Lancashire, whose register commenced in 1677 ; but now there 
were upwards of fifteen hundred observers in various parts of Great 
Britain. The subject of rainfall had received great attention from 
Mr. G. J. Symons, who published annually tables of the rainfall in all 
parts of this country, and also from the British Association, which had 
appointed a Rainfall Committee, the results of whose labours were 
most valuable. One of the most interesting and practical problems 
which had been discussed by the Rainfall Committee was ‘‘ the secular 
variation of rainfall since 1725.” ‘The mean rainfall having been 
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