[ u ] 



the mafles of the original ftony appearance, to which thofe glafles 

 were reduced by flow cooling, were foftened in degrees of heat 

 of from 32° to 45° ; to the formation of thefe lafl he conflantly 

 applies the term cr^dlization and calls them cryflalites. To the 

 vague term of cryllallization I muft however objed, for as thofe 

 ftones in their original ftate prefent no regular cryftals, but are 

 at moft internally and imperfectly cryftallized, fo they mufl be 

 when reduced from a glafly ftate to one refembling their original 

 and thus difcover rather a nifus towards cryftalization than 

 perfeft cryftals, which latter the term cryftallization generally 

 applied would lead us to expect. 



Before I proceed to the detail of thefe experiments, I muft 

 obferve that the different fufibilities of thefe eryjlalites, as he calls 

 them, indicate a very different ftate from that in which they 

 originally exifted ; the former requiring a heat of from 32" 45' 

 and the latter a heat of from 38" to 55^, the reafon of whic 

 is eafiiy difcovered when the two ftates are deduced from i 

 different origination, but is in vain fought for, when both are o 

 be deduced from one and the fame origin. 



Passing over the general preliminary accounts of thefe-x- 

 pcriments, which are to be found from p. 7 to p. 10 o/^his 

 differtation, I ftiall now examine the moft important partii^ars 

 of each, as far as they give occafion to any ftriking obferv'ons. 

 In this examination I am much affifted by the ingeniou' accu- 

 rate 



