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EDINBURGH MAGAZINE,

OR

LITERARY MISCELLANY,

FOR FEBRUARY 1800.

With a View of MELVILLE-CASTLE, the Seat of the Right Hon. Henry Dundas, E.

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THE

EDINBURGH MAGAZINE,

OR

LITERARY MISCELLANY,

FOR FEBRUARY 1800.

ACCOUNT OF EXPERIMENTS ON WHINSTONE. BY SIR JAMES HALL, BART. F. R. S. & F. A. S. EDIN.

[From the Tranfactions of the Royal Society of Edinburgh.]

THE experiments defcribed in this paper were fuggelted to me many years ago, when employed in ftudying the Geological Syftem of the late Dr Hutton, by the following plaufible objection, to which it seems liable.

Granite, porphyry, and bafaltes, are fuppofed by Dr Hutton to have flowed in a ftate of perfect fufion into their prefent pofition; but their internal ftructure, being univerfally rough and ftony, appears to contradict this hypothefis; for the refult of the fufion of earthly fubftances, hitherto obferved in our experiments, either is glass, or poffeffes, in fome degree, the vitreous character.

kingdom, which he has thus reconciled to his fyftem.

One neceffary confequence of the pofition of thefe bodies, feems, however, to have been overlooked by Dr Hutton himself: I mean, that, after their fufion, they must have cooled very flowly; and it appeared to me probable, on that account, that, dur ing their congelation, a cryftallization had taken place, with more or lefs regularity, producing the ftony and cryftallized ftructure, common to all unftratified fubftances, from the large grained granite, to the fine grained and almost homogeneous bafalt. This conjecture derived additional probability from an accident fimilar to thofe formerly obferved by Mr Keir, which had juft happened at Leith: a large glafs houfe pot, filled with green bottle glafs in fufion, having cooled flowly, its contents had loft every character of glafs, and had completely affumed the ftony ftructure.

This objection, however, lofes much of its force, when we attend to the peculiar circumstances under which, according to this theory, the action of heat was exerted. These fubftances, when in fufion, and long after their congelation, are fuppofed to have occupied a fubterraneous pofition far below what was then the fur- These views made part of a paper face of the earth; and Dr Hutton which I had the honour of laying behas afcribed to the modification of fore the Society in 1790; and about heat, occafioned by the preffure of the fame time I determined to fubthe fuperincumbent mafs, many im- mit my opinions to the teft of expe portant phenomena of the mineral riment. communicated this intenL 2

tion

tion to all my friends, and in particular to Dr Hutton; from him, how ever, I received but little encouragement. He was impreffed with the idea, that the heat to which the mineral kingdom has been expofed was of fuch intenfity, as to lie far beyond the reach of our imitation, and that the operations of nature were performed on fo great a fcale, compared to that of our experiments, that no inference could properly be drawn from the one to the other. He has fince expreffed the fame fentiments in one of his late publications, (Theory of the Earth, vol. I. p. 251.) where he cenfures those who "judge of the "great operations of the mineral kingdom, from having kindled a "fire, and looked into the bottom of "a little crucible."

But, notwithstanding my veneration for Dr Hutton, I could not help differing from him on this occasion: For, granting that thefe fubftances, when in fufion, were acted upon by a heat of ever fo great intenfity, it is certain, nevertheless, that many of them must have congealed in moder ate temperatures, fince many are eafily fufible in our furnaces; for it is impoffible that a fubftance should congeal at a higher point than that at which it may afterwards be melted. If, then, thefe phenomena depend upon the circumftances of congela. tion, the imitation of the natural procefs is an object which may be purfued with a rational expectation of fuccefs; and, could we fucceed in a few examples on a small fcale, and with eafily fufible fubftances, we should be entitled to extend the theory, by analogy, to fuch as, by their bulk, or by the refractory nature of their compofition, could not be fubjected

to our experiments. It is thus that the aftronomer, by obferving the ef fects of gravitation on a little pendulum, is enabled to eftimate the influence of that principle on the heavenly bodies, and thus to extend the range of accurate fcience to the extreme limits of the folar system.

Encouraged by this reafoning, I began my projected series of experiments in the course of the same year (1790,) with very promifing appearances of fuccefs. I found that I could command the refult which had occurred accidentally at the glasshouse; for, by means of flow cooling, I converted bottle glafs, after fufion, into a tlony fubflance, which again, by the application of strong heat, and fubfequent rapid cooling, I reftored to the ftate of perfect glass. This operation I performed repeatedly with the fame fpecimen, so as to afcertain that the character of the refult was ftony or vitreous, according to the mode of its cooling.

Some peculiar circumstances interrupted the profecution of thefe experiments till laft winter, (1798) when I determined to refume them. Deliberating on the fubftance most proper to fubmit to experiment on this occafion, I was decided by the advice of Dr Hope, well known by his difcovery of the Earth of Strontites, to give the preference to whinftone.

*

The term whinftone, as ufed in most parts of Scotland, denotes a numerous clafs of ftones, diftinguished in other countries by the names of bafaltes, trap, wacken, grünftein 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

*In the course of laft winter, when I first thought of refuming my experiments, I propofed to this gentleman, that, in imitation of a practice, common in the Academy of Sciences of Paris, we should perform 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 bestow upon the fubject the time which it neceffarily required; and we gave up the idea of working in company.

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