at Leith Fort, every Hour of the Day, in 1824- and 1825. 25 



riod of its descending motion is 14 h 20' ; the heat of the day, 

 therefore, advances with more rapidity than the cold of the 

 night. 



The daily curve of 1825 is projected in a similar manner 

 in Plate V., Fig. 27, from the last column of Table IV., and 

 forms the upper curve of the plate. Each point of it is the 

 mean of 365 observations. Its resemblance and general pa- 

 rallelism to that of 1824, cannot fail to strike the reader, and 

 proves how nearly these observations have conducted us to 

 the form of the daily curve. 



The intermediate curve, which is laid down from the last 

 column of Table VI., and is the mean of the two curves, is 

 nearly free from the very slight inequalities in the afternoon 

 branch of both curves, and may be considered as representing, 

 with great accuracy, the mean annual daily curve for the la- 

 titude of Leith, and at the level of the sea. 



In order to observe the variation in the form of the daily 

 curve in different seasons, I have given, in several plates, their 

 projections for every month in 1824 and 1825, and the mean 

 of the monthly curves in 1824 and 1825 ; but we must refer 

 for these plates to the original memoir. 



By taking the means of the six Summer months, from April 

 to September inclusive, and of the six Winter months, from 

 October to March inclusive, and projecting them in the usual 

 manner, we obtain an accurate type of the daily progression 

 of temperature in Summer and Winter, each point of each 

 curve being the mean of about 180 observations. 



The summer curve descends regularly from midnight till 

 4 o'clock in the morning, when the coldest time of the day 

 occurs, and it ascends with great regularity till 3 o'clock, 

 when it commences a very rapid descent to its minimum, 

 the total mean range being about 8°.61. 



The winter curve, on the contrary, has a gentle rise from 

 1 a. m. till 2 a. m. It then descends till 6, when it com- 

 mences its ascent, reaches its maximum at 2, and again de- 

 scends, but more slowly than it rose, the greatest difference of 

 temperature being about 3°86. 



The difference of character in the curves of April and Oc- 

 tober deserves to be noticed. Although these months arc 



