Dr. Bostock on Evaporation. -315 



The quantity of evaporation during an hour, from a circular area 

 of water of two inches in diameter, taking the average of 130 ex- 

 periments performed on different days, of which 93 were made 

 during the winter months, from November to March, both inclusive, 

 and 37 during the summer months, from Rlay to September, both 

 inclusive, is .5596 grains ; or, taking the average of the first 37 

 winter observations which occur in the Journal, and of the 37 

 summ-er observations, the quantity will be '634 gr. per hour. 



The average of the 93 winter observations is '421 gr., or of 

 the first 37 which occur in the Journal, -4223 gr. ; the average of 

 the 37 summer observations, is '908 gr. per hour. 



With respect to the comparative rate of evaporation during the 

 different months, the following are the averages of 149 experi- 

 ments, chiefly performed during single hours on different days. 



The experiments, as appears by the Journal, were frequently 

 continued for more than one hour on the same day, when, as cir- 

 cumstances allowed, the results were either examined at the end of 

 each successive hour, or an average was taken of the whole. In 

 this way, the Journal contains the results of 1188 hours, the ave- 

 rage of the whole of which is "501 gr. per hour. Of these 942 

 were during the winter months, and 246 hours during the summer. 

 The average of the 942 winter hours, is '43 gr., of the 246 summer 

 hours '77 gr. I am not aware of any cause which will account for 

 the winter evaporation appearing to be greater in this case, than 

 when the average of single hours on different days is taken. We 

 perceive, on the contrary, that the average of the summer evapo- 

 ration is less than that indicated from the experiments performed 

 on single hours ; perhaps, this may depend on the operation in the 

 former case having been protracted until late in the evening; and, 

 in a few instances, carried on during the night, whereas the single 

 experiments were generally performed during the forenoon 



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