CHAPTEE XIX 



WEDGWOOD'S PYROMETER OR THERMOMETER 



EVER since Wedgwood had begun the manufacture of 

 earthenware, his attention had been attracted to the 

 heat of his kilns. He pulled down one after another 

 in order to find the furnace that would bake his earthen- 

 ware and melt his glazes. This cost him a great deal 

 of money, but he conquered the difficulty by his usual 

 perseverance. 



He experimented constantly, in the endeavour to 

 find the necessary gradations of heat up to the very 

 highest point ; and this led him to the invention of his 

 pyrometer that is, a machine for measuring tempera- 

 ture by the expansion of solid bodies by heat. He 

 began from the commencement of redness up to the 

 highest temperature that can be produced in the 

 furnaces of the chemist. The celebrated Bergmann, in 

 his Sciagraphia, reckoned the heat at which silver 

 melts to be less than that which makes iron red hot. 

 This, however, was afterwards found to be a mistake. 



