Prof. Bischoff' on Hot and Thermal Spr'mffs. 331 



Rubio,* is 82°.09 Ft, the minimum being in January 80°.35, and 

 consequently their difference 1°.73. Supposing the temperature 

 of the air at Cumana, in the beginning of the rainy season, to 

 be at the mean or even below it ; if the rains be still colder, they 

 must cool the air until the equilibrium be restored. But thf 

 rains will cool the earth's crust, so far as they penetrate into it, 

 sooner than they will the air : and, after some time, both the air 

 and the earth will assume the temperature of the rains. In order 

 to be able to observe the progress of the changes of temperature 

 in the air and in the soil, I made the following experiments. 



I placed a thermometer in a glass cylinder 20 inches high, 

 and suspended in it a second, in such a manner, that the bulb 

 was 10 inches above the bottom of the cylinder. This thermo- 

 meter was protected by a small bell-glass, which was so luted on 

 to it, that the bulb just appeared below its edge. The thermo- 

 meter at the bottom shewed 70°. 70 ; that suspended in the air, 

 69°.8. I then let the water of 54°.50 fall in a fine shower into 

 the cylinder, and quickly observed the following alterations of 

 temperature. 



Thermometer 



In the air, . . 69°.8 67°.55 Ce°.20 61°.2u 51*'.0 59°.0 

 On the bottom, . 70°.70 59°.9 59°.45 68°.55 58°.35 58°.32 



At this moment I was obliged to interrupt the experiment, as 

 a drop of water had spirted on to the bulb of the suspended 

 thermometer and caused the mercury to fall to 58°.55. Had this 

 not happened, there is no doubt that the thermometer in the ^r 

 would soon have fallen as low as the one on the bottom of the 

 cylinder. Similar changes must take place in the earth and air 

 during the fall of rains. 



Now if the cooling of the soil keeps even pace with that of the 

 air during the winter rains, and if the only difference is, that the 

 former is somewhat in advance of the latter, the yearly mean 

 temperature of the soil can be depressed but imperceptibly be- 

 low that of the air by this cause. When the winter rains cease, 

 the temperature of the air soon begins to rise again ; but the 

 earth remains longer at its lowered temperature on accoiuit of 

 the evaporation. This lower temperature may perhaps last ra- 



• Annal. de Chimie el de Phys. voL xxii. p. 303.^ 



t We again remind the reader that the degrees in this memoir are ac- 

 rordinp; to Fahrenheit's scale, cxceptinji; where otherwise stated. 



