Imatges de pàgina
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· The tourmalin and a veffel of charged glass hermetically sealed are both excited by heating and cooling. What other properties have they in common ?

• IV. Concerning Electrification. · Does electrification increase the exhalation of vapours, either from cold or from boiling water ? If it do, is the increased exhalation the same in all states of the atmosphere ?

· Does not the electric matter pass chiefly on the surfaces of bodies?

• Is the action of electrified bodies upon one another more properly an attraction, or a repulsion ?

• Would not continued electrification promote putrefaction ?

• In what manner is the mutual repulsion of two bodies electrified negatively performed ? Is it by the attraction of the denser ele&ric fluid in the neighbourhood, or by the quantity of it which may be supposed to be accumulated on the surfaces of such bodies ?

V. Concerning the Power of Charging Electrics. • What is the real operation of conductors in coating electric substances ?

Why may not one phial be charged by connecting it with another (while it is charging) as high as if it were charged at the prime conductor ? Or by what rule must the force of those different chargings be estimated ? To all appearance, two phials charged together, so as that one of them receives the fire from the other, do not give so large a shock, as only one of them charged in the usual way.

• What is the maximum of charging a glass jar, with respect to the quantity of its surface, covered by the coating? It is evident that some jars will discharge themselves, when only a finall part at the bottom of them is coated, and when the explosion is very inconsiderable.

Endeavour to charge a plate of glass with the coating pressed into actual contact with its surface, by means of heavy weights. Also endeavour to excite a plate of glass in the same

It is pretty certain that, in the usual method of exciting and charging, the real substance of the glass is not touched ; and though water be attracted by glass, it may, only be to a certain distance from it.

• VI. Concerning the Ele&tricity of Glass. Through what thickness of glass will an excited electric, of any given strength, attract and repel light bodies ? Is not the same thickness the limit of charging the glass with the electric fluid ?


• Is not a plate of glass contracted in its dimensions by charg. ing, the two electricities strongly compressing it, so as to increase its specific gravity ?

• Is the tone of a glass veffel, made in the form of a bell, the same when it is charged as when it is uncharged ? Or would the ringing of it make it more liable to break in those circumstances ?

• Does the electric Auid with which glass is charged reside in the pores of the glass, or only on its surface ; or rather within the space that is occupied by the power of refraction, i. e. a fmall space within, and likewise without the surface ?

• Is the refractive power of glass the same when it is charged or excited ?

• How does the different refra&ive power of glass, or its density (which is probably in the same proportion with its refractive power) affect its property of being excited or charged ?

• Is there not a considerable difference in glass when it is new made, and when it has been kept a month or two, both with respect to excitation and charging ?

• Let glass of every different composition be tried both with respect to excitation, and charging. Would it not be found that differences with respect to metallic ingredients, hardness, annealing, continuance in fusion, &c. would influence both the properties; and that, in several cases, the same circumstance that was favourable to one would be unfavourable to the other?

• Glass has hitherto been supposed to be full of the electric fluid, and its impermeability has been accounted for upon the difficulty with which the electric fluid moves in its pores. But may we not suppofe the substance of glass to be absolutely impermeable to electricity, that no foreign electric matter ever so much as enters a single pore of it, but lodges wholly on its surface ; for instance, between the point of contact and the real surface, or within the limits of the refractive power that is a little way on both sides the surface. This place is, I think, on many accounts, extremely convenient to dispose of the electric matter, whether we make it to consist of two fluids, or of one. Their being kept asunder, if there be two, or its being prevented from getting through, if there be but one, will be much easier to conceive in this case, than upon the supposition that the electric fluid can enter and move in the substance of the glass, though it can only enter and move with difficulty, as Æpinus exprefies it. For, let the motion be ever so dif ficult, one would think, that this circumstance could only make it move fo much the lower, and that, give the electricity

in the charged plate of glass time enough, and it would, at length, without any external communication, perform the journey to the other side, whither it has so strong a tendency

to go.

Moreover, one would think, that, upon the hypothesis of the admission of the electric fluid within the pores of the glass, when the discharge of a phial was actually made thro the substance of the glass, it might be in a filent manner, without breaking the glass ; whereas when the surfaces of the glass are supposed to be violently pressed, and the pores of it not in the least entered by any particle of the fluid, or fluids, the impossibility of the electric charge getting through the glass is evident, as well as the neceflity of its breaking the glass, if it do force a passage. * VII. Concerning the Effect of Ele&ricity on Animal

Bodies. * Is the fluid on which ele&ricity depends at all concerned in any of the functions of an animal body? In what manner is the pulse of a person electrified quickened, and his perfpira, tion increased ?

• Does not the air, by being heated in the lungs, communicate an electric virtue to the blood ? What connection has this circumstance with the mephitic air which is exhaled from the lungs in great quantities, as well as contained in all the other excrements of the animal body ?

May not the increased perspiration of an animal body be greater in a moist atmosphere than in a dry one, there being then more conducting particles in the atmosphere, to act and react upon the effluvia in the pores of the body ; on which the copious perspiration does, probably, in a great measure, depend?

• VIII. Concerning the Electricity of the Atmosphere. • In what manner do the clouds become possessed of electricity ?

• Does the wind in any measure contribute to it?

• Is it effected by the gradual heating and cooling of the air ? If so, whether is it the heating or the cooling that produces positive electricity ? Which ever it be, the contrary will probably produce negative ele&tricity. Let the experiment be made by an electrical kite. Mr. Canton.

• As thunder generally happens in a sultry state of the air, when it seems replenished with some sulphureous vapours ; may not the electric matter then in the clouds be generated by


the fermentation of sulphureous vapours with mineral or acid vapours in the air.

Mr. Price. • Let rain, snow, and hail be received in insulated vessels, in different states of the atmosphere, to observe whether they contain any electricity, and in what degree.

May not the void space above the clouds be always occupied with an electricity opposite to that of the earth ? And may not thunder, earthquakes, &c. be occasioned by the rushing of the ele&tric fluid between them whenever the redundancy in either is excessive ? Is not the aurora borealis, and other eleco trical meteors, which are remarkably bright and frequent before earthquakes, fome evidence of this?

• Is not the earth in a constant state of moderate ele&rification, anel is not this the cause of vegetation, exhalation, and other the most important processes in nature ? These are promoted by increased ele&rification. And it is probable that earthquakes, hurricanes, &c. as well as lightning, are the confequence of too powerful an electricity in the earth.'

We have transcribed these queries and hints, in preference to any other part of the book, because we apprehend they will be of most general advantage to those who are engaged in electrical enquiries, by shewing them that, though much has been done, there remains yet much unaccomplifhed. Some of these problems are indeed difficult of solution ; but there are many of them which are by no means beyond the reach of experiment.

In part the fifth, our author treats of the construction of electrical machines, and the principal parts of an ele&rical apparatus. Part the sixth contains practical maxims for the use of young electricians. In part the seventh we have a description of the most entertaining experiments performed by electricity ; and in part the eighth we are presented with several new experiments made by the author in the year 1766. These experiments are most of them curious, entertaining, inftru&ive, and important. In short, the whole book is evidently the work of an indefatigable and ingenious philofopher, and is by far the most comprehensive produ&ion on the subject of electricity.

III. Medical Essays and Observations. By Charles Bislet, M. D.

8vo. Pr. 55. Dodíley. OCTOR Biffet is already known in the republick of let

ters by his treatise on the Scurvy, and his Essay on the Medical Constitution of Great Britain. The diseases particularly considered in this volume are the bilious fever of the



West Indies, the nervous 'colic, symptomatic tetanus, ophthalmia, iliac passion, dysuria, St. Vitus's dance, hooping-cough; worms, land-fcurvy, hypochondriac affection, fcorbutic itch; and dropsy of the knee ; to which is added, a chapter of chirurgical observations. He has also a chapter of physiological enquiries relative to perspiration, &c. another, containing obfervations relative to putrefaction, and the concoction of peccant humours in fevers ; another on the West Indian air; and another containing the theory of the periodical fea and landbreezes in hot climates, which last mentioned chapter begins his book. This philosophical disquisition, and the diseases peculiar to the West Indies, not being of general importance, we shall pass them by unnoticed, and proceed to chapter the fixth, containing observations and reflections relative to putrefaction, &c, in which the Doctor controverts the prevailing opinion, as he calls it, that certain malignant fevers do wholly result from a putrid fermentation of the circulating juices excited by a putrid ferment; and likewise the notion, which at present is so prevalent, that putrefaction is the chief immediate cause of most fevers.' What the prevalent opinion may be in the county of York, we do not pretend to know ; but this opinion is far from prevailing in the southern part of the kingdom: and with regard to malignant fevers, that they wholly result from a putrid fermentation, excited by a putrid ferment, it is fo far from being a general opinion, that we do not believe it was ever advanced by any writer of character. That putrid fevers are often infectious, is most certain ; and that, in case of infection, the disease is produced by a putrid ferment, is most rational, which is all that authors have asserted. He confesses, indeed, that the smell of putrid animal substances hath fometimes given rise to malignant fevers ; in which case, he supposes, that the fever was partly excited by a peculiar influence of the effluvia on the olfactory nerves, but chiefly by the inAuence of sympathy or antipathy. If the doctrine of fermentation cannot be admitted for want of demonstration, the Doctor's hypothesis must appear much less admissible on the fame account. In fupport of his opinion, “ In diseases, says he, acquired by infection, particularly the small-pox and measles, some particles only of the juices are aliimilated to the nature of the infectious miasmata ; but were these to operate as a putrid ferment, the whole mass of blood would be alike distempered ; and, in this case, no separation of the peccant humour, or an eruptive crisis, could poflibly take place. So that, according to this hypothesis, no separation can take place, if the whole mass be affected: the very contrary of wh happens to be true in every instance of fermentation, where the VOL. XXIII. May, 1767,



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