246 Josiah Wedgwood CHAP. 



belt's scale, from which it appeared that the greatest 

 heat he could generate in a small furnace coincided 

 with many thousands of degrees of Fahrenheit, the 

 scale of heat which was registered by his Thermometer 

 being about thirty-four times as extensive as that to 

 which the common Thermometers could be applied. 



In another paper (Phil. Travis. Ixxvi.) he described 

 the manner of forming the clay pieces and of adjusting 

 the quality of the clay itself, with the divisions of the 

 measuring gauge or scale, so that the same circum- 

 stances might constantly give the same results. The 

 clay he had employed at first was the small remainder 

 of a parcel from Cornwall, which was soon exhausted. 

 Fresh parcels, even from the same pit, differed con- 

 siderably in the degree of their diminution by fire. 

 He therefore found it necessary to add to the best clays 

 he could procure a large proportion of Alum earth, in 

 the gelatinous state in which it was precipitated by 

 alkalies from the solution of alum, and well washed by 

 boiling water. By these and other experiments, Wedg- 

 wood was at length enabled to bring his clay to the 

 proper degree of compression, so as to be duly measured 

 by his heat gauge. 



Wedgwood had much correspondence with Sir Joseph 

 Banks, President of the Koyal Society. Many of Sir 

 Joseph's early letters consisted of introductions of 

 distinguished foreigners to Wedgwood, whose works 

 at Etruria were considered one of the shows of the 

 kingdom. One of the most interesting was the letter 



