356 SIR DAVID BREWSTER ON THE HOURLY 



The general results which may be deduced from the preceding Tables 

 relate — 



1. To the form and character of the annual and monthly daily curves, or the 

 daily progression of temperature. 



2. To the arrangement of the monthly curves in separate groups. 



3. To the determination of the times of the day when the mean temperature 

 occurs. 



4. To the relation between the mean temperature of the day, and that of any 

 single hour or pair of similar or homonymous hours. 



5. To the parabolic form of the four branches of the annual daily curve. 



I. On the Form and Character of the Annual and Monthly Daily Curves, or the Daily 



Progression of Temperature. 



The mean temperature of the year 1826 was 48°436, and that of 1827 48°-407, 

 both of them intermediate between that of the two preceding years ; but though 

 in its average character the temperature of 1826 was moderate, yet it differed 

 from both of them in a remarkable manner. Though the mean annual curves of 

 1824 and 1825 differ from one another, from the former representing a cold and 

 the latter a warm year, yet they are perfectly parallel, indicating the same 

 vicissitudes of climate. The curve of 1826, however, exhibits the character 

 of an American climate, descending almost as low as that of 1824 in the 

 morning branch, and rising nearly as high as 1825 in the warm period of the 

 day. 



The curve for 1827 differs remarkably from that of 1826, keeping above it 

 from 1 o'clock in the morning till 8 o'clock in the evening, but almost touching it 

 at the morning and evening hours of mean temperature. See Plates XXIV. and 

 XXV. ' 



In all the curves for these four years, the lowest temperature took place at 

 5 o'clock in the morning. The temperature increased, with great regularity, till 

 3 o'clock in the afternoon, when it descended to its minimum. The period, 

 therefore, of its ascending is ten hours, and that of its descending motion fourteen 

 hours. 



By comparing the summer and winter curves or the mean temperatures of 

 the six summer months, from April to September inclusive, with those of the six 

 winter months, from October to March inclusive, as exhibited in the annexed 

 Table, we are enabled to discover whether or not the peculiar character of 1826 

 is derived from the warm or the cold season. 



