max. t. + min. t. + t. at 9 hours + t. at 21 hours4
(2) The mean monthly daily range of temperature, or what is practically as valuable, the mean maxima and minima.
(3) The “relative humidity” of the air, or the proportion of moisture actually present to the amount that would suffice to produce saturation, for each month of the year.
(4) The monthly rainfall.
(5) The number of rainy days in each month.
(6) The average condition of the sky, whether clear or overcast, in each month.
(7) The amount and daily distribution of wind, its direction being for us of little moment.
In speaking of air temperatures it must always be understood that temperatures in the shade are referred to, and in systematic scientific observations the greatest care must be taken that not only shall the instruments be thoroughly protected from the direct, but also from the reflected rays of the sun; and that means are also taken to secure a free current of air over them.
If an absolutely exact determination of the temperature of the air in any given situation be required, the observation should be taken by swinging the instrument, attached to a short cord, rapidly round the head, and by this method it is possible to secure a close approximation to the actual air temperature, even in the open and under the direct rays of the sun.
In considering the effects of climate on human beings it will be well to commence with a short consideration of the way in which they are affected by each of these elements of climate.