XI. Description of a Barometer, which marks the Rise 

 and'EA'LL of the Mercury from two different Times of 

 Observation. By Alexander Keith, Efqj F. R. S. & 

 F. A. S. Edin. 



yRead Jan. ^. 1796.] 



IN Auguft laft, I read to this Society the Defcription of an Air 

 Thermometer, intended to record the various degrees of 

 heat at every inftant; and mentioned my intention of conftrudl- 

 ing a barometer, which would, in the fame manner, record the 

 variations of the weight of the atmofphere : Both which I pro- 

 pofed to adapt to one piece of clock-work. 



This piece of machinery appearing too complicated and ex- 

 penfive for general ufe, I contrived a thermometer, which marks 

 the extreme points of heat and cold from any two times of ob- 

 fervation. Of which inftrument I alfo lately read an account, 

 and produced the machine itfelf. 



I NOW intend further to lay before this Society the defcrip- 

 tion of a barometer upon fimilar principles, of a very fimple con- 

 ftru<flion, which alfo marks the variation of the atmofphere 

 from one time of obfervation to another. 



Vol. IV. C c Fig. i. 



