38 Temperature of the Year. 



changes during what may be termed a mean annual day. Its 

 maximum is near 2, P. M., its minimum about 5, A. M., and its 

 range 14°.61. 



In this annual curve, the small irregularities of the monthly 

 curves balance each other, and disappear. Its upper half is sym- 

 metrical, and has very nearly the form of a parabola. But in tra- 

 cing the two branches from the vertex to the minimum point, it 

 will be perceived that the inclinations of the lower parts are very 

 unequal, the night portion sloping much more gradually than the 

 morning portion. The same thing is indicated by the fact, that 

 between the points of minimum and maximum temperature, there 

 intervene only nine hours in the morning, but fifteen hours in 

 the afternoon and night. 



The straight horizontal line, near 47°, expresses the mean tem- 

 perature of the year, and crosses the last named curve, so as to 

 make the sum of the vertical ordinates above it equal to those be- 

 low. 



Another curve is introduced, which has no connection with 

 the hours marked at top and bottom. On the second vertical line 

 is placed a small mark at 22°. 94, the mean temperature of Janu- 

 ary; on the fourth, another mark at 28°. 57, the mean tempera- 

 ture of February, and so on. These marks are then connected 

 by a continued curve, which therefore expresses the annual range 

 of the monthly means. Each small mark through which the 

 curve passes, is the place where might be drawn a horizontal line, 

 that would be obtained from the corresponding monthly curve, 

 by reducing its vertical ordinates to an average. The horizbntal 

 line near 47°, already noticed, bears the same relation to this as 

 to the other annual curve ; in each, the sum of the ordinates above 

 the straight line is equal to the sum below. 



An inspection of the curves, as well as of the table, shows that 

 January was the coldest, and July the warmest month of the 

 year, as is usually the case ; that the temperature of March and 

 November was nearly equal ; also that of February and Decem- 

 ber ; that the mean of the whole year differed less from that of 

 April than any other month ; and that seven months were warmer, 

 while onXj five were colder than the annual mean. It is notice- 

 able, also, that in summer the mean daily range is three or four 

 degrees greater than in winter. 



