. 106 THE ROYAL ‘SOCIETY OF CANADA 
The year may be considered a natural period of time, representing 
as it does, the time occupied by the earth in traversing its orbit 
around the sun. In extratropical regions the year consists of two 
distinct seasons, namely, a warmer or summer season, and a colder 
or winter season. Spring and autumn are merely transitional periods 
between the seasons of maximum and minimum temperatures. If 
the year is divided equally between these two seasons the six warmer 
months in the northern hemisphere will extend from May to October 
and the six colder months from November to April. These periods 
accordingly are taken as the summer and winter seasons in the present 
discussion. 
The month, representing approximately the time taken to com- 
plete the phases of the moon may be regarded as a fairly natural 
period. 
As the average year consists of 365 days and some hours it is 
obviously not possible to divide it into equal parts. But under the 
present arrangement the month of February is an anomaly and there 
appears to be no satisfactory reason why each of the twelve months 
should not consist of either 30 or 31 days. As, however, the reports 
of the Meteorological Service are made out in terms of the months 
as they stand I have adhered throughout to the present system. 
The day is also a natural unit representing the time taken for one 
complete revolution of the earth on its axis. The week is an artificial 
period of time and would serve a useful purpose if it were of such 
a length that the weeks could be grouped into months without leaving 
any odd days. As this is not possible I have in consequence discarded 
it as a time-unit. In any scheme of dividing the months into shorter 
time-periods of a number of days each it will be an advantage to have 
an even number of such periods so that climatic data for half the 
month may be readily available if desired. The choice, therefore, 
lies between a three-day and a five-day period and the five-day 
period has been adopted as the most suitable intermediate time- 
period between the day and the month. The months will consequently 
be divided into six periods of five days each. Where the month 
contains 31 days the last period will contain six days. The last 
period in February will contain three days, or in a leap year four 
days. As the length of the year makes it impossible to divide it into 
12 months of exactly equal length, so it is impossible to divide a month 
of 31 days into exactly equal parts. 
The hour, although an artificial unit, is a useful measure of time 
for indicating fractions of a day. 
The daily record will of course form the basis for most generalisa- 
tions on the subject of climate. 
