VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 383 



observations were made, is 104-° above freezing, by the same scale of Reaumur. 

 There appears not therefore any necessity for an internal heat ; on the contrary, it 

 is matter of demonstration, that were there any source of heat in the earth which 

 was not equally in the air, the heat of the interior parts ought to be higher than 

 a mean : and if the central heat bore as high a proportion to that of the sun as 

 M. de Mairan alleges, the heat of the earth itself ought to be a great deal above 

 the mean temperature of the air, which from observation there is no ground for 

 believing. It is easy to see the source of M. de Mairan's error ; he has founded 

 his calculations on the scale of Reaumur, and considers the degrees of his ther- 

 mometer as marking the real proportions, and absolute quantity of heat. It is a 

 matter that cannot be denied, that we know nothing of the absolute quantities of 

 heat ; and that the degrees of our thermometers are only to be considered as a 

 few of the middle links of a chain, the length of which we are totally ignorant of, 

 and therefore in no condition to compare its proportional parts. It deserves how- 

 ever to be remarked, that observations of a late date have shown, that the notions 

 of cold on which Reaumur's scale was constructed, and on which M. de Mairan's 

 calculations are founded, are imaginary and without foundation. 



The sea admits of change of temperature more quickly than July 63^° 

 the earth, particularly near the shore. The mean heat of the Aug. 634-° 

 sea at Brighthelmstone, during the months of July, Aug. Sept. Sept. 58" 

 and Oct. was as annexed : Oct. 53° 



The wells at New York are from 32 to 40 feet in depth, and Dr. Nooth found 

 them to have an annual variation of 2°, from 54° to 56°. There are few coun- 

 tries, in which the annual range of the thermometer is greater than at New 

 York, and the neighbouring parts of America. In the summer it is often as 

 high as 96°, and in winter it has been observed several degrees below the zero of 

 Fahrenheit's scale. On the whole, we may, from all the observations we are yet 

 in possession of, conclude, that there is at present no source of heat in the earth, 

 capable of affecting the temperature of a country, which is not derived from the 

 sun ; and that the earth, whatever changes of temperature it may be conjectured 

 to have undergone in former periods, is now reduced to a mean of the heat pro- 

 duced by the sun in different seasons, and in different climates. 



