82 
any idea from the temperature of a winter what kind of 
summer temperature may follow. 
I have shown on the same diagram the mean tempera- 
ture of each year from 1861 to 1878. The mean of all is 
48‘0 deg. The ratios of their differences are extremely 
small, so small indeed as to be of no practical value ; for 
between the coldest year and the warmest of the last 17 
years there is a difference of only 2*9 deg., and the mean 
difference of temperature of all these years amounts to only 
0 3 deg. These differences do not, from the data I have, 
seem to observe any definite rule. 
