sm 



THIRD REPOUT — 1833. 



in general proportions. They may also be compared with an 

 excellent sei'ies of dew point observations in the Manchester 

 Memoirs by my friend Mr. John Blackwall, whose results in 

 other respects I have found remarkably in accordance with my 

 own inferences concerning the climate of York. 



Now, let m be taken inversely as the mean range of tempe- 

 rature, (r) or m = a we shall have the following 



So remarkable and continued an accordance between the co- 

 efficients fixed by observation and those derived by two methods 

 from a very simple view of the condition of the air as to heat 

 and moisture, appears to me decisive of the question as to 

 the o-eneral cause of the variation of the quantity of dimimition 

 of rain at any one height above the ground. It has already 

 been shown how strictly the observations warrant the con- 

 clusion that the ratio of diminution at different heights is con- 

 stant through the whole year. It is therefore rather as a 

 matter of very probable inference than a plausible speculation 

 that I offer the hypothesis, that the whole difference in the 

 quantity of rain, at different heights above the surface of the 

 neio-hbouring ground, is caused by the continual augmentation 

 of each drop of rain from the commencement to the end of its 

 descent, as it traverses successively the humid strata of air at 

 a temperature so much lower than that of the surrounding me- 

 dium as to cause the deposition of moisture upon its surface. 

 This hypothesis takes account of the length of descent, because 

 in passing through more air more moisture would be gathered ; 

 it agrees with the fact that the augmentation for given lengths 

 of descent is greatest in the most humid seasons of the year ; 

 it accounts to us for the greater absolute size of rain-drops in 



