134 HEAT OF LOWEST STRATUM OF AIR. 



ing degrees of the thermometer are marked on 

 straight lines drawn at right angles to the former 

 at these points, and likewise divided into 

 equal parts (for the ordinates). By this mode, 

 twenty-four points are obtained, which, when 

 connected by a continuous line, give a very clear 

 graphic representation of the daily range, enabling 

 you to ascertain by simple inspection the time 

 of occurrence of the daily maximum and mini- 

 mum, as well as two daily mean values. — In 

 central Europe, the lowest temperature of the day, 

 taking one day with another, is generally found 

 a little before sunrise; the highest in summer 

 about three o' clock, and in winter between one 

 and two in the afternoon. Of the mean tempera- 

 tures, one falls between eight and nine in the 

 evening, and the other between eight and ten in 

 the morning. 



The curved line which represents the course of 

 the temperature encloses with its abscissae and ordi- 

 nates a number of small figures, of which the sum is 

 equal to a rectangle, whose base is the abscissa 

 representing the length of the day, and whose 

 height is the arithmetic mean of the twenty-four 

 ordinates. This shows the correctness of the 

 process, which is universally adopted, of deducing 

 the mean diurnal temperature of the day, from 

 the arithmetic mean of the observations made at 



