334 Prof. Bisclioff on the Temperature of 



between 63°,50 and 62°.82, and 5,625 lbs. of water were filtered 

 through the sand. 



Third Series of Experiments with very Wet Sand. 

 Time _ 5 6 9 13 17 18^ 21 22 25 28 m 



Water 61°.70 _ 61°.25 61°.47 — — 61».47 — 61°.70 — 61°.70 

 Sand 100 .95 99 .50 98 .37 96 .35 90 .50 81 .50 79 .25 74 .75 72 .27 68 .67 66 .20 

 Water 1 



filtered \ 76 .10 82 .40 86 .00 92 .30 92 .52 91 .85 91 .40 90 .50 90 .05 89 .60 87 .35 

 through J 



Time 30 34 38 42 44 48 50 54 57 60 m 



Water 61».70 _ 61°.93 _ _ 62M5 _ 62°.37 62°.37 e2°.37 



Sand 64.17 63.50 63.05 62.60 62.60 62.37 62.37 62.37 62.37 62.60 



Waterl 



filtered \ 86 .00 81 .95 79 .92 75 .20 73 .85 70 .25 69 .57 67 .55 66 .65 (jQ .20 



through } 



The tenaperature of the air fluctuated, during the experiment, 

 between 65°.30, 65°. 75, and 64°.62 ; and 7 lb. of water were 

 passed through. 



The results of the two first experiments shew, that water, 

 passing from a certain height through a layer of sand of a lower 

 temperature, gives up almost all its excess of temperature above 

 that of the sand, and passes off with nearly the same tempera- 

 ture as the sand originally had. But this only holds good for a 

 certain quantity of water, and a certain length of lime ; for 

 when the whole layer of sand has acquired the temperature of 

 the water, the water must pass off with its own original tempe- 

 rature. 



The third series exemplifies the contrary case; namely, when 

 a cold rain falls upon a heated soil. Here also the sand de- 

 creases in temperature more considerably and more rapidly than 

 the percolating water. The temperature of the sand continu- 

 ing lower than that of the water after the filtration, was, how- 

 ever, caused by my only being able to observe the temperature 

 of the sand at ten inches below its surface, on account of the 

 shortness of the tube of the thermometer, the whole height of 

 the column of sand being fourteen inches. It is true, so great 

 a difference as 71°.15 F., between the temperatures of the soil and 

 the rain, which we assumed in the third series of experiments, 

 is seldom to be met with in nature. However, De Luc once 

 observed a fall of temperature at Geneva o{ 63°.50 F., caused by 

 rain. 



The surface of the bell-glass, containing the sand, was equal 

 to 17.7 square inches; and, considering the water filtered 



