Dec, 1845.] 297 



of rain guaged was 10.17 inches; the evaporation from the sur- 

 face of the pond was 15.07 inches, showing the evaporation to be 

 48.1 per cent, more than the depth of rain. By an average of five 

 periods of observation into which this time was divided, the ratio 

 of water derived from the slopes, to the rain which fell upon them 

 was .1765 to 1., or the actual depth was 1.79 inches. Conse- 

 quently, the evaporation from the land, and from its vegetable 

 covering, was .8235 of the rain which descended. Hence the 

 ratio between the evaporation from land, and that from water, was 

 .8235 : 1.48l=.55G : 1. 



In the district of Long Pond, 18 miles south west from Boston, 

 from the 30th of July to the first of November, the depth of rain 

 was 10.46 inches; and of evaporalion 12.78 inches — conse- 

 quently the evaporation was 22.2 per cent, more than the rain. 



The water derived from the slopes of the district was .1839 of 

 the whole fall of rain, leaving .8161 : 1 as the proportion evapora- 

 ted from the land, or appropriated by vegetation, and the ratio of 

 evaporation from land to that from the water, was consequently 

 .8161 : 1.222= .667 : 1. 



It appears from comparisons of the annual falls of rains for long 



periods-of years, that the quantities of rain above stated, as having 



fallen in the months of August, September, and October last, at 



the two sources mentioned, are about the average quantities due 



to those months, and that consequently the ordinary ratio which, 



in the neighborhood of Boston, and at the season above specified, 



may be expected to flow from the land, and be available in water 



. .1765+. 1839 1ono , , no 



sources is =.1802 or almost exactly 18 per cent. At 



other seasons, very different proportions between the quantity of 

 rain, and that of evaporation, would be found to prevail. Whether 

 in the winter season, the same ratio would be found to exist be- 

 tween the evaporation from land, and that from a water surface, as 

 has been found to prevail in summer, is a question still awaiting 

 a practical, experimental determination. The same methods of 

 research, as have been applied in the above cases, would be found 

 applicable to its solution, substituting only in part the fall of snow 

 guaged as water for that of rain, and the evaporation from a sur- 

 face of ice for that from a surface of water. 



The elevated and insulated position of Spot Pond, resting in a 



