170 CHEMISTRY. 



it at like distances, continually augments the effect. 

 With an obstruction of one case, the rate of refrige- 

 ration is three times slower ; with two cases, it is five 

 times slower ; with three cases, seven times slower ; 

 and so on as expressed by the succession of odd 

 numbers. 



Concentrated Cold. 



A piece of frozen quicksilver the size of a walnut, 

 dropped into a tumbler of warm water, occasions its 

 instant congelation, accompanied with the fracture of 

 the glass. 



Artificial Cold. 



The greatest artificial cold that has yet been pro- 

 duced, was effected by the mixture of diluted sul- 

 phuric acid with snow, which sunk Fahrenheit's ther- 

 mometer to minus 91, or 123 below the freezing 

 point. 



Bengal Ice. 



From experiments in procuring ice, Dr. Wells 

 found reasons for inferring, that water may freeze at 

 night in air of a temperature higher than 32, without 

 any loss from evaporation ; and he concludes, that 

 the formation of ice in Bengal must be attributed to 

 a loss of heat which the water suffers by its own 

 radiation, and not from evaporation. 



Latitude and Elevation. 



A degree of latitude, in France, may be reckoned 

 as affecting the mean temperature, nearly in the pro- 

 portion of 180 and 200 yards of elevation. 



Perpetual Congelation. 



The never-melting snows begin under the equator 

 at 2460 fathoms above the level of the sea ; under 

 the 20th degree north or south latitude, at 2350 ; 



