Meteorological Observations at Hudson, Ohio. 329 



The average annual amount of rain is by these observations 

 34.635 inches ; yet this period includes an extraordinary drought 

 in the autumn of 1S3S. It is presumed that the mean of a long 

 series of years would be about 36 inches. This is the average 

 for the State of New York according to the Regents' Reports. 

 The average amount at Hanover for four years is 38.05 inches ; 

 so that with a much less degree of cloudiness, it has a greater 

 amount of rain than Hudson. The amount of rain here is great- 

 est in summer and least in winter, being in the inverse ratio of 

 the degree of cloudiness ; and what is still more remarkable, in 

 December, which is the most cloudy as well as most humid 

 month of the year, the fall of rain is the least. The stratus 

 cloud then which prevails in winter throughout all the Lake coun- 

 try, must evidently have a peculiar origin. I ascribe it to the 

 evaporation from the Lakes. During the winter season, and espe- 

 cially the month of December, these vast collections of water are 

 warmer than the land ; the water which evaporates from them 

 is immediately condensed, forming a hazy cloud which spreads 

 all over the neighboring territory. This explains an anomaly to 

 which I have already alluded (p. 325), that it sometimes snows 

 here uninterruptedly for a week, with the thermometer about 

 30^, and during the entire period there will not be sufficient snow 

 to whiten the ground. It appears also that more rain falls in the 

 day than in the night. The observation at 9 A. M. includes the 

 rain of eighteen hours, and that at 3 P. M. of six. The for- 

 mer then should be three times the latter, which is not the case 

 except in winter, which period I exclude from the comparison, 

 because the precipitation being mostly snow, which cannot be 

 collected in a gauge, I am accustomed at the conclusion of each 

 snow storm to collect what appears to me to be the average depth 

 of snow and melt it. This operation is most frequently per- 

 formed in the morning, and hence the excess of rain at 9 A. M. 

 in the winter. During the rest of the year, however, and espe- 

 cially in summer, there is a considerable excess in favor of 3 P.M. 

 If the observations had been made at 6 A. M. and P. M. they 

 would have better exhibited the ratio for the two periods. The 

 inequaUty however is sufficiently palpable, as during summer, the 

 amount of rain from 9 A. M. to 3 P. M. is one half of that from 

 3 P. M. to 9 A. M. 



Vol. xLi, No. 2.— July-Sept. 1841. 42 



