EPOCH OF DE LISLE AND HAUY. 227 



mention his separation of the sulphates of baryta 

 and of strontia, which had previously been con- 

 founded. Among crystals which in the collections 

 were ranked together as " heavy spar," and which 

 were so perfect as to admit of accurate measure- 

 ment, he found that those which were brought 

 from Sicily, and those of Derbyshire, differed in 

 their cleavage angle by three degrees and a half, 

 "I could not suppose," he says 7 , "that this dif- 

 ference was the effect of any law of decrement ; 

 for it would have been necessary to suppose so 

 rapid and complex a law, that such an hypothesis 

 might have been justly regarded as an abuse of the 

 theory." He was, therefore, in great perplexity. 

 But a little while previous to this, Klaproth had dis- 

 covered that there is an earth which, though in 

 many respects it resembles baryta, is different from 

 it in other respects ; and this earth, from the place 

 where it was found (in Scotland), had been named 

 Strontia. The French chemists had ascertained 

 that the two earths had, in some cases, been mixed 

 or confounded; and Vauquelin, on examining the 

 Sicilian crystals, found that their base was strontia, 

 and not, as in the Derbyshire ones, baryta. The 

 riddle was now read; all the crystals with the 

 larger angle belonged to the one, all those with the 

 smaller, to the other, of these two sulphates ; and 

 crystallometry was clearly recognized as an autho- 



7 Traitt, ii. 320, 



