Chemical Philosophi;. 105 



thermometer is said to be the most ingenious, 

 simple, and perfect of any which has hitherto ap- 

 peared. 



It was still, however, an important desidera- 

 tum to find some easy and exact method of 

 measuring very high degrees of heat. Such a me- 

 thod was not long since invented by Mr. Wedge- 

 w^ooD, of Great-I3ritain, a gentleman well known 

 for his great improvements in the art of pottery. 

 After many experiments,''' he produced an instru- 

 ment which he called a pyrometer, and which, by 

 means of the contraction of clay, marks, with much 

 precision, the different degrees of heat, from 947*^ 

 of Fahrenheit's scale, to the greatest heat of an 

 air-furnace. 



It was first observed by Dr. Black, that dif- 

 ferent bodies have different capacities for imbibing 

 and retaining heat. The fact was afterwards no- 

 ticed, and the subject further investigated, by 

 Drs. Irvine and Crawford, and by Professor 

 WiLCKE, of Stockholm. The last named gentle- 

 man called the quantity of caloric necessary to 

 raise the temperature of substances a given num- 

 ber of degrees, their specific heat. For measuring 

 this heat an instrument was contrived by Messrs. 

 De la Place and Lavoisier, and called by the 

 latter a calorimeter ; the nature and value of which 

 will be found exhibited in various books of che- 

 mistry. 



Another instrument, invented in modern times, 

 and which has engaged much of the attention oif 

 chemists, is the eudiometer. This instrument was 

 invented by Dr. Priestley, and is used for as- 

 certaining the purity of the atmospherical air, or 

 the quantity of oxygen contained in it, which is 

 indicated by the diminution of its volume on being 



m Sw Fhiioso^hleal Transactions for 178^, X784, l^%6, 

 P 



