ftyr the Tfiermometer. 419 



he had produced by a mixture of ice and salt, which he 

 at that time btheved to be the greatest degree of coljj in 

 nature*. 



There is no scale which I have met with, which seems 

 to have been founded upon the principle I have adopted : 

 thermometers indeed have been constructed in England, 

 for particular purposes, in which was placed at what was 

 supposed to be the middle state of the air in this climate ; 

 but this principle is of too local and vague a nature to 

 merit attention. 



I know of one objection, only, which can be started 

 against the adoption of the alteration in the scale I have 

 proposed, viz. the too frequent occasion, as might be 

 urged, for the use of the plus and minus characters ; but 

 the fact is, that in a scale founded upon this principle, 

 there is less occasion than ever for the use of either of 

 them, as must be apparent to any one upon the least re- 

 flection. 



For meteorological observations this scale will be parti- 

 cularly appropriate ; the zero in this instance being the 

 mean temperature of the greatest heat and greatest cold 

 experienced in the hottest and coldest climates, collectively y 

 ae well as in the temperate climates f. 



At Quito in Peru, which is peculiarly situated between 

 the extremes of heat and cold, the temperature of the air 

 is uniformly, or with very little variation, throughout the 

 year at 62 of Fahrenheit; and this is considered to be the 

 healthiest spot in the world %- 



If we had no means of correcting or regulating the tem- 

 perature of our apartiTients by fire, we should find a few 

 degrees, viz. ten below the point of 62, much more un- 

 comfortable than the same difference above 62; and in a 

 difference of thirty degrees from that point the cold would 

 be intolerable, in the first instance; whereas at thirty abovey 

 no considerable inconvenience is experienced : but the dif- 

 ference would be exactly the inverse of each other, were it 



* sir Isaac Newton's thermometer was constructed in 1701, and Fjjh- 

 renheit's in 1724. 



f In some parts of Africa the thermometer rises sometimes up to ll2 alovc 

 62 of Fahrenheit, viz. 174, and in some jmrts of North America it some- 

 times sinks to 1 12 lelow 62 of Fahrenheit, viz. —50. A similar circumstance 

 takes place in the temperatt or middle climates ; thus in England the ther- 

 mometer rises sometimes to 126, and sometimes sinks to— 2jViz. a dif- 

 ference, each way, of 64 degrees. 



\ The mean annual temperature of Quito is 6^'y and the utmost limits 

 of variation throughout the year are from three or four degrees below that 

 point, to as many degrees above it. 



D d 2 not 



