Daniell on Meteorological Observations. Ill 



of the sun are still very iucomplete ; but I cannot help hoping, 

 that when sufficiently advanced, they will afford matter for useful 

 speculation. What is the difference of the effect in different 

 years ? What are its effects in maturing the fruits of the earth ? 

 What is its connexion with the production of vapour ? How is 

 its energy spent when veiled from the earth by clouds ? Its 

 average for the half year, from March to August, was 27° above 

 the mean highest in the shade, its maximum effect 144°. 

 Many reflections readily suggest themselves upon this subject, 

 but it would be premature to indulge in them at present. 



The mean constituent temperature of the vapour stands in an 

 interesting relation to the other particulars of general tem- 

 perature. Its connexion with the average of the mean is very 

 obvious, and it appears to be influenced, in some measure, by 

 the mean lowest, which it never exceeds by more than 41°. 

 The average degree of dryness for the whole twenty-four hours, 

 by this comparison, would appear to be 1° below that obtained 

 by the three direct experiments, and the correction before 

 applied. But it must be remembered, that although the force 

 of the vapour is affected by the maximum cold of the night, 

 the degree of dryness is not liable to its influence. After the 

 point of humidity is once attained, which it generally is long 

 before the minimum, a further reduction of temperature does 

 not alter the circumstances ; so that an observation of the 

 lowest temperature of the night as included in the general 

 mean temperature, is not applicable to this purpose. 



I have now, in conclusion, a few remarks to make upon the 

 comparison of the two years. They will not be found to differ 

 much in their general averages, but in their particulars very 

 materially. The year 1819 — 1820 was, however, drier than 

 the year 1820 — 1821, and a greater depth of rain fell, in 

 the latter than in the former. The first was also distinguished 

 very much more by extremes than the second, all the instru- 

 ments except the barometer denoting a very much wider 

 range. 



The autumns differed very essentially in their characters, 

 la the first half-quarter the year 1819 was 1:J° drier, and 2|° 



