74 BOARD OF AGRICULTURE. 



with water. Evaporation from the leaves of plants is very con- 

 siderable ; some vegetables transmitting- more than half their 

 own weight daily. We are now very far from absolute knowledge 

 in this direction, and possibly at our best estate may not be 

 materially wiser. The observed phenomena on a few square or 

 cubic yards of earth must be insufficient data from which to reason 

 upon the meteorology of a State. It is safe to say that no one can 

 now tell what percentage of precipitation is evaporated ; what 

 carried down to the sea by superficial channels ; what absorbed by 

 the ground and carried ofi" by subterranean conduits ; what drawn 

 from the earth or the air by a given extent of forest, of short pas- 

 ture vegetation, of tall meadow grass, or a crop of cereals or any 

 other farm product ; what given out again by surfaces so covered, 

 or by bare ground of various textures and composition, under dif- 

 ferent conditions of atmospheric temperature, pressure, and humid- 

 ity ; or wh.at is the amount of evaporation from water, ice, or 

 snow, under the varying exposures to which they are subjected in 

 actual nature. But divesting the subject of the labyrinth of diffi- 

 culties with which it seems beset, there are seen some simple facts 

 that are of interest in this connection. 



The subject matter of aqueous downfall, evaporation, and the 

 excess of the former, so far as it retires by superficial channels — 

 representing the water-power of the State — will probably be 

 treated at length in the Eeport of the Hydrographic Survey. It is 

 not within the scope of our present efibrt, to trench farther upon 

 this ground than is necessary to elucidate the few and simple 

 positions that follow. 



From observations made near Philadelphia, the amount evapo- 

 rated from water surface in one year was 32.88 inches. The 

 amount deposited as rain and snow in the same year, 43.19 inches. 

 During the summer months of the same year, 18.62 inches evapo- 

 rated, and but 8.03 inches deposited. At Ogde'nsburg, N. Y., in 

 one year, 19.94 inches were evaporated in the summer months, 

 and for the year, 49.31 inches. At Syracuse, N. Y., in one year 

 23.53 were evaporated in the summer, and 50.20 inches during the 

 year. At Salem, Mass., as the result of extended observations, 

 the annual evaporation amounted to 56 inches ; and the same 

 result is reported from Cambridge. From many calculations made 

 at Baltimore, the average evaporation for the summer is 19.91 

 inches — about twice as much as the rain-fall in the same time. 

 Observations made at the Agricultural College of Michigan, for 



