Effects of Temperature. 1 33 



in a vessel of boiling water. The mercury instantly fell to 

 212°, and then very gradually sunk to 141°, The merino 

 envelope had become dry, and the mercury had commenced 

 rising when the bulb was immersed a second time into the 

 water. The mercury rose to 202°, and then gradually fell 

 to 139°. By a third immersion the mercury rose to 198°, 

 whence it fell gradatim to 133°. The envelope was now sa- 

 turated with water at about 140° Fahrenheit, but the mercury 

 speedily reassumed the temperature of 133° Fahrenheit, and 

 remained at this fixed point for nearly five minutes, although 

 the real temperature of its situation was, and had been for 

 many previous hours, 310° Fahrenheit. 



The effects of rapid aqueous evaporation were thus clearly 

 shown to influence the indications of the thermometer when 

 placed in a dry atmosphere of 310° Fahrenheit, and under 

 the circumstances described, to the surprising extent of 177° 

 Fahrenheit. 



We may now infer that the copious perspiration which ex- 

 udes from the skin of glass-makers, and of those who are en- 

 gaged in similar scorching occupations, is a sufficient protec- 

 tion from the burning effects of a dry atmosphere of from 

 300 to 400 degrees of Fahrenheit ; and that whilst the clothes 

 of such persons are burning to tinder, their skin may be ren- 

 dered insensible to the direct effects of fire upon the inani- 

 mate matter around them, by simple natural laws, viz. those 

 of evaporation. 



Having been engaged in some delicate experiments on the 

 subject of heat, I was surprised at the effects of comparatively 

 moderate dry temperatures upon such thermometer scales as 

 were made of ivory. 



In one instance the scale became shortened two degrees in 

 100 in a temperature of 212° Fahrenheit. 



In another, an old and "well-seasoned" ivory scale that 

 had often endured the maximum solar heat of Jamaica and 

 the salt waters of the Atlantic, became shortened one decree 

 in 110° from a dry temperature of ]30° Fahrenheit. 



In a third, the scale became shortened 11° in 120° from a 

 short exposure to a dry heat of 260° Fahrenheit. Immersion 

 in water will generally restore such scales to their original 

 length. 



I have the honour to be, Gentlemen, 

 yours obliged, 



Wraxall, near Bristol, CHARLES THORNTON CoATHUPE. 



April 22, 1840. 



