14 PHILOSOPHICAL TRANSACTIONS. [aNNO 1744. 



Fahrenheit is the first who has remarked the contrary. He observed that the 

 heat of boiling water was greater when the air was heavy, that is, when the mer- 

 cury stood higher in the barometer; and, on the contrary, the heat was less when 

 the air was lighter. M. Le Monnier the younger, has put Fahrenheit's discovery 

 past all doubt, and has very much improved it. 



On the 6th of October 1739, being provided with a barometer, and a mercurial 

 thermometer of M. Delisle, he climbed up to the highest top of the C&nigou, a 

 mountain in Roussillon, esteemed the highest among the Pyrenees: there he 

 found his barometer to stand at 20 inches 2-^ lines ; while at Perpignan it stood at 

 28 inches 2 lines. The difference between the heat of the water which he boiled 

 there, and that which he boild at Perpignan, was 15 degrees of his ther- 

 mometer. 



The same thermometer being surrounded with snow, the mercury fell down to 

 the same degree as pounded ice had made it do at Paris. Hence he concludes, 

 that the heaviness of the air has a sensible influence on boiling water; but that it 

 in no way alters the term of congelation. 



This same experiment Mr. S. repeated on the top of the Pic du Midy; think- 

 ing that so singular a fact ought to be observed more than once. He carried two 

 barometers to the highest top of the Pic du Midy on the Qth of last July; the 

 mercury rose in one of the barometers to 20 inches 2 lines ; and in the other, to 

 20 inches 1^- line. He surrounded his thermometer with snow, and the mercury 

 fell exactly to the same degree as the snow had made it fall to at Bagneres. After- 

 wards he plunged it into boiling water; on which the mercury rose to l65° of his 

 graduation: so that the difference between the heat of boiling water on Pic du 

 Midy, and that at Bagneres, consisted of 1 5° ; of which there were 180 between 

 the marks of congelation and boiling water. 



At his return to Bourdeaux, he observed that he had marked the term of boiling 

 water at Bagneres less high by 3-^, than at the term of boiling water at Bourdeaux, 

 taken at the time when the barometer was at 28 inches 2 or 3 lines : therefore 

 having anew graduated the thermometer, the l65th, the degree of the former 

 graduation, fell now on the l62d; so that the complete difference between the 

 term of boiling water on the top of the Pic du Midy, and that of the same at 

 Bourdeaux, the barometer being at 20 inches 3 lines, amounts to 1 8 degrees on the 

 thermometer of Fahrenheit. 



Now the conformity between the observation made by M. Le Monnier, and this 

 repetition of the same observation, can hardly be greater; seeing the heights of 

 the barometers are almost the same; and the 15 degrees of difference, found by 

 M. Le Monnier on De Lisle's thermometer, amount precisely to 18 degrees on 

 the thermometer of Fahrenheit. 



