I am glad my remarks on your observations met with your approbation. If you think they will at all illuftrate the fubject, the Society have my full permiffion to do what they please with them; if they should not think they will take more room than they deferve, I fhall esteem their approbation a great honour. But they

will seem to ftand infulated and alone, and perhaps will not be perfectly intelligible, unless they are introduced by your obfervations, which were the cause of them.

The more I reflect upon the fubject, the more I am convinced of the power and extent of the influence of attraction in chemical phænomena. In folution, it has been admitted ever fince the time of Sir Ifaac Newton; but there are many other facts, which the late experiments on elaftic fluids lead us to explain in the fame manner.

I fhall, in this letter, only have time to exemplify this pofition, by directing your attention to the circumftances, which take place in the CALCINATION OF METALS. The experiments of Stahl, &c. convincingly prove, that metals in calcination part with the phlogifton; and those of Mr. Lavoifier fhew, that the calx of a metal, thus deprived of phlogifton, is not merely an inert earth, but that it is the bafe of the metal united with the aërial acid, or fixed air. It is obvious,

obvious, therefore, that in the process, the action of the fire expels the phlogifton from the metallic earth, which then attracts the aerial acid, either floating in the air, or generated by the fire, and continues united with it, till by proper circumstances of application the phlogiston is again brought to act on the metallic calx, and to unite with it; and the aerial acid being expelled the metallic is revived. This, then, is one of those cafes of elective attraction, which is varied by the degree of heat. To prove that what I have faid above is juft, let us examine another mode in which metals are deprived of their phlogifton, that is, by folution. A metal, perfectly diffolved in its proper acid menftruum, is held in folution, till some substance is added, which has a greater attraction to one of the ingredients, than they have to each other. Thus, a mild alkali added, attracts the acid, and the metallic earth is precipitated. It is a calx, in all circumftances the fame, as that obtained by perfect calcination and here it also indifputably contains the aerial acid. Indeed, we in a manner fee it take poffeffion of the fixed air in the process: for when the alkali is added, and attracts the acid, no effervefcence enfues, though we know the alkali parts with its air, whenever it unites with an acid. It is therefore certainly abforbed by the precipitated calx, and with that, by experiment, we find it united. Again, if we add to a folution of any VOL. II. G g metal

It

metal in an acid, another metal which has a stronger attraction for that acid, we know that the former metal will be precipitated, and the latter taken up in its place: and the former will be precipitated, not in a calcined, but in a metallic ftate; because, in this inftance, the precipitated metal attracts the phlogifton, of which the other metal is deprived by its folution. appears therefore that the whole bufinefs of the calcination and reduction of metals depends upon the laws of fingle or double elective attraction, either fimply in folution, or as they are affected and varied by heat. It appears too, how nearly thefe proceffes are connected with the doctrine of the elaftic fluids, with which we are fo lately made acquainted; for the properties of fixed air are fully established; and I think, the more recent experiments of Dr. Priestley, &c. go near to fhew, that the phlogiston of metals, if not exactly the fame, is certainly nearly the fame, as inflammable air.

On

On the VOLUNTARY POWER which the MIND is able to exercife over BODILY SENSATION. By THOMAS BARNES, D. D. Read November 3, 1784.

THE

HE mutual action of the body and the mind upon each other is felt every moment. The knowledge of the nature, effects, symptoms, and measures of these reciprocal influences, forms no inconfiderable part of the science moft neceffary to the phyfician, the moralift, and the divine. It enters deeply into every study, of which either body or mind is the profeffed fubject. And whatever difficulties may attend our inquiries, in the way of mere. theory and fpeculation-difficulties which arife from the narrow limits of the human faculties, and from the abfurd attempt to investigate the effences, rather than the operations, of nature-yet we may acquire from EXPERIMENTS and FACTS a knowledge, clear in its evidences, certain in its principles, and important in its application.

The question which I have proposed to confider, "Whether the mind has any kind of voluntary

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luntary power over bodily fenfation, is not merely speculative. It must be determined by an appeal to facts; and its influence is, in a high degree, practical and interesting.

SENSATION is generally defined to be-" A perception in the mind, excited by means of the organs of fenfe, independently on the will." Thus, when my eye is open, external objects make an impreffion; nor is it in the power of my mind, if the organ is found, to exclude the vifion. In like manner, the touch, the tafte, the fimell, produce their correfpondent feelings, which the mind paffively receives, because it is not able to repel them. If this be true of pleafant, it is ftill more true of painful fenfations. Over thefe, it is faid, the will has no controul. Sense will be fenfe; and pain will be pain, notwithstanding all our endeavours to blunt the acuteness of the one, and the anguish of the other.

This fentiment, though true to a certain point, is not however fo abfolutely and invariably true, as to admit of no limitation. Many strong facts prove, that the mind is not fo entirely the flave of fenfe, as to have no power at all to fufpend, or, at least, to moderate its impreffions. many inftances, fhe is able to exercise fome measure of that regency, which her nature and office authorize her to maintain over her material and mortal partner.

In

Senfation