42 INTRODUCTION. 



raife it above ^6, The medium heat of the water of 

 the fprings, therefore, feems to be the fame as the 

 medium heat of the open air : But the water of the 

 fprings is much lefs liable to change than the air is, 

 inafmuch as the caufe of the changes in both, 

 cannot operate with the fame, freedom on the one, 

 as it does on the other. 



The greateft degree of cold I ever obferved, was 

 on Tuefday,^ the 21 ft of February 1792 : At feven 

 o'clock in the morning of that day, the mercury 

 flood at 7, and it rofe no higher that day than 25, 

 although the fun flione bright all day. And the hotteft 

 day I ever took notice of, was Sunday the 7th of July 

 1793, a regifter of which is to be feen in my journal. 



It appears, from a regifter of the thermometer 

 kept at London by Dr. Heberden, for nine years 

 (that is, from the end of 1763 to the end of 1772), 

 that the mean heat, at eight in the morning, was 

 47 ; and by another regifter, kept at Hawkhill, 

 near Edinburgh, that the mean heat in that place, 

 during the fame period of time, was 46. By 

 regifters kept in London, and at Hawkhill, for the 

 years 1772, 1773, 1774, it appears that the mean 

 heat of thefe three years in London, at eight in the 

 morning, was 48 ; and at two in the afternoon, 

 ^6 : And the mean heat of three years, both morn- 

 ing and afternoon, 52. And the mean heat at 

 Hawkhill, for the fame time, at eight o'clock in the 

 morning, was 45 ; and at two in the afternoon, 

 50 : And the mean heat for the morning and 

 afternoon, for the whole time, 47. The mean 



heat 



