Chap. 3 .] Mode ofmeafuring high Degrees of Heat. 1 1 5 



fions of which may be eafily taken) in that furnace, 

 and, when heated, to plunge it into a quantity of cold 

 water, and multiply the degree of heat by the propor- 

 tion which the bulk of the water bears to that of the 

 body heated. Thus, if a piece of iron is taken red hot, 

 and thrown into a quantity of water 100 times its bulk, 

 when the heat which v/as concentrated in the iron is 

 diffufed through the whole quantity of water, it is evi- 

 dent that the temperature of the water thus heated, 

 multiplied by 100, will give the heat of the iron when 



' red hot. 



Another mode of afcertaining high degrees of heat 

 has been propofed by the late Mr. Wedgwood, who 

 by means of a diftinguifhing property in argillaceous^ 

 bodies, namely, that of contracting when expofed to 

 fire, was enabled to conftruct a new thermometer for 



, this purpofe. The fenfible contraction of earthen- 

 ware commences at a low red heat, and proceeds re- 

 gularly till the clay becomes vitrified. Mr. Wedg- 

 wood's thermometer, therefore, confifts of a fmall por- 

 tion of this clay, properly baked, and fo nicely adapt- 

 ed to a brafs gage, that the clay is permitted to flide 

 along the gage in proportion as it is contracted by the 

 fire. He divided his fcale, from the degree of heat at 

 which the clay begins to contract, to the greateft de- 

 gree of heat he was able to produce, into 160. By 

 this inflrument he found, that copper melted at 27 i 

 filver at 28 i gold at 32} caft iron at 130*. 



