X. Description of a Thermometer, which marks the great- 

 ejl Degree of Heat and Cold, from one Time of Ob- 

 servation to another, and may alfo regijler its own 

 Height at every Instant. By AleXjINDER KElTHy 

 Efqi F. R. S. & F. A. S. Edin. 



" {Read Augujl 3. 1 795.] ^ 



THERMOMETERS have hitherto been defeaive for meteo- 

 rological purpofes, in fo far as they only point out the de- 

 gree of heat at the moment of infpedling them, but do not fhow 

 ■what the difference of temperature has been, from the time of 

 one obfervation to that of another : Nor has any inflrument 

 been yet conftruAed, fo far as I have been able to learn, whick 

 will record the intermediate degrees of heat. 



The ingenious Robert Hook, in the end of the lafl century, 

 - mentions his intention of making a thermometer for the above, 

 purpofe ; but it does not appear that it was ever executed : Nei- 

 ther does he explain how it was to have been done. 



The thermometer, invented by M. James Six, as defcribed 

 in the yad volume of the Philofophical TranfuBions of the Royal 

 Society of London, is made to fliow its greatefl rife or fall from 

 one period of obfervation to another. This is done by means 

 of two fmall pieces of black glafs, which float on two different 



B b 2 furfaces 



