lo Experiments on Whin/lone and Lava, 



is Impoffible that a fubftance fliould congeal at a higher poinc than that at which it may 

 afterwards be melted. If, then, thefe phenomena depend upon the circumftances of con- 

 gelation, the imitation of the natural procefs is an objeiSl which may be purfucd with ra- 

 tional expetStatioij of fuccefs : and could we fucceed in a few examples on a fmall fcale, 

 and with eafily fufiblc fubftances,'we fliould be entitled to extend the theory, by analogy, 

 to fuch as, by their bulk, or by the refra£lory nature of their compofition, could not be 

 fubje£led to our experiments. It is thus that the aftrononier, by obl'erving the efFefts of 

 gravitation on a little pendulum, is enabled to eftimate the influence of that principle on 

 tfie heavenly bodies, and thus to extend the range of accurate fcieuce to the extreme limits 

 of the folar fyftem. 



Encouraged by this reafoning, I began my projefled feries of experiments in the courfe 

 of the fame year ( 1 790), with very promifing appearances of fuccefs; I found that I could 

 command the refult which had occurred accidentally at the glafs-houfe ; for, by means of 

 flow cooling, I converted bottle glafs, after fufion, into a ftony fubftance, which again, 

 by the application of ftrong heat, and fubfequent rapid cooling, I reftored to the ftate of 

 perfect glafs. This operation I performed repeatedly with the fame fpecimen, fo as to af- 

 cettain that the chara£ier of the refult was ftony or vitreous, according to the mode of its 

 cooling. 



Some peculiar circumftances interrupted the profecution of thefe experiments till laft 

 winter, when I determined to refume them. Deliberating on the fubftance moft proper to 

 fubmit to experiment on this occafion, I was decided by the advice of Dr. JJope *, well 

 known by his difcovery of the earth of ftrontites, to give the preference to whinftone. 



The term whinftone, as ufed in moft parts of Scotland, denotes a numerous clafs of 

 ftones, diftinguilhed in other countries by the names of bafaltes, trap, wacken, grlinftein 

 and porphyry. As they are, in my opinion, mere varieties of the fame clafs, I conceive 

 that they ought to be connected by fome common name, and have made ufe of this, already 

 familiar to us, and which feems liable to no obje£lion, fince it is not confined to any par- 

 ticular fpeciesf. * 



The following experiments were performed with various kinds of whinftone, and have 

 likewife been extended to lava. To inveftigate the relation between thefe two clafles of 

 fubftances, feems, in the prefent ftate of geology, an obje£l: of confiderable importance ; 

 for they referable each other in fo many refpefls, that we are naturally led to afcribe the 



• III the courfe of laft winter, wheu I firft thought of refuming my experiments, I propofed to this 

 trentleman, that, in imitation of a praftice, common in the Academy of Sciences of Paris, we fliould per- 

 form them in company. To this propofal he cheerfully agreed ; but, before any experiments had been 

 begun, he found himfelf fo much occupied by profeffional duties, that he could not beftow upon the fub- 

 ieft the time which it neceflaiily required ; and we gave up the idea of working In company. 



•f- In charailerifing the particular fpecimens, I have adopted, with fcarcely any variation, defcriptions 

 drawn up by Dr. Kennedy, whofe name I (hall hare occafion frequently to meution in the courfe of this 

 paper. In the employment of terms, we have profited by the advice of Mr. Deriabii), a gentleman well 

 Tcrfed in the language of the Werneriau fchool. 



formation 



