EPOCH OF DE LISLE AND HAUY. 323 



oreviously been confounded. Among crystals which in the collections 

 were ranked together as "heavy spar," and which were so perfect as 

 to admit of accurate measurement, he found that those which were 

 brought from Sicily, and those of Derbyshire, differed in their cleavage 

 angje by three degrees and a half. " I could not suppose," he says, 7 

 " that this difference 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 discovered 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 belong to the one, all those with the smaller, to the other, of 

 these two sulphates ; and crystallometry was clearly recognized as an 

 authorized test of the difference of substances -which nearly resemble 

 each other. 



Enough has been said, probably, to enable the reader to judge how 

 much each of the two persons, now under review, contributed to crys- 

 tallography. It would be unwise to compare such contributions to 

 science with the great discoveries of astronomy and chemistry ; and 

 we have seen how nearly the predecessors of Rome and Haiiy had 

 reached the point of knowledge on which these two crystallographers 

 took their stand. But yet it is impossible not to allow, that in these 

 discoveries, which thus gave form and substance to the science of crys- 

 tallography, we have a manifestation of no common sagacity and skill. 

 Here, as in other discoveries, were required ideas and facts ; clearness 

 of geometrical conception which could deal with most complex rela- 

 tions of form ; a minute and extensive acquaintance with actual crys- 

 tals ; and the talent and habit of referring these facts to the general 

 ideas. Haiiy, in particular, was happily endowed for his task. With- 

 out being -a great mathematician, he was sufficiently a geometer to 

 solve all the problems which his undertaking demanded ; and though 

 the mathematical reasoning might have been made more compendious 



7 Traite, ii. 320. 



