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The daily range in Great Britain in summer is from 12° to 15° in the West and Midland districts, and from 18° to 20° in the South. In the dry climate of Madrid it will sometimes amount to 30°.
The daily range is greater over land than over water, for there is more radiation (disturbance of temperature) from land than from water.
The mean temperature of any given day is the mean of twenty-four hourly observations, but observations at the following hours nearly supply the mean of the day:—
(1.) Between 8 and 9 a.m. and p.m. in the summer.
(2.) Between 9 and 10 a.m. and p.m. in the winter.
| (3.) The Mean of | 4 a.m. 10 a.m. 4 p.m. 10 p.m. |
6 a.m. 2 p.m. 10 p.m. |
7 a.m. Noon. 10 p.m. |
(4.) And generally, the mean of four observations at equal intervals will give the mean for twenty-four hours; as also will the mean of maximum and minimum, without an error, as a rule, of one degree.
When three observations are made daily, the best hours are 9 a.m., 3 p.m., and 9 p.m. The observation at 3 p.m., being near the time when the temperature is at its highest, is of great value in reference to the climate of a locality, as well as in reference to other considerations of more strictly scientific interest.
The mean of observations at hours of the same number (or name) a.m. and p.m. do not
