Note 128 — Chapter XXI
Reading edition
The mean of any number of unequal quantities is equal to their sum divided by their number: thus the mean temperature of the air at any place during a year is equal to the sum of the mean temperature of each month divided by 12. This method, however, will only give an approximate value; therefore, to ascertain the mean annual temperature at any place accurately, the mean of a number of years must be taken.