Imágenes de páginas

ways equable, and, at all times, equal to the mean motion ; whence the place of the sun being, known at any certain time fixed, his place, at any other time afligned, would be readily computed. But Astronomers, by comparing together the places of the sun deduced from observation, have found, that the apparent motion of the fun through the ecliptic is unequal, and that he moves swifter through some parts of it than through other's ;; that his apparent motion is, sometimes, 61 minutes nearly, at others, scarce 57 minutes, and that he is nearly seven days longer in moving froin the first point of Aries through the northern half of the ecliptic, to the first point of Libra, than from thence through the southern half of the ecliptic, to the first point of Aries.

The ancient Astronomers, who allowed of no other motion in the heavens than what were circular and equal, that they might account for these inequalities in the sun's motion, and adjust the several quantities of it in several parts

of the orb, supposed that the fun moved round the earth in a circular orb, but excentrical'; that is, whose center was at fome distance from the center of the ecliptic, in which they placed the earth; and that this circular orb was described by an equal motion, so that a line or ray drawn from the center of the orb to the fun, described equal areas in equal times.)

But the great Kepler, by comparing the observations of the famous Tycho together, discovered, that Mars was not carried round the sun in a circular, but in an elliptic orb; that the sun was placed in one of the foci of that ellipsis, and that in moving, round the fun his motion was to regulated, that a ray of light drawn from the sun to the planet, described an elliptic area, or space, always proportionable to the time. This induced him to examine whether the motions of the other planets regulated by the same law; and having satisfied himself that they were, he concluded, that it was realonable to suppose, that the earth also observed the same law, and moved round the an elliptic orb; and this having been confirmed by all observations made since his time, there is no room left to doubt of the truth of it.--And, therefore, as the earth in her annual motion round the fun, is governed by the equal and uniform description of areas, which increase and decrease uniformly with the time, it is imposible she can every where move with the same uniform velocity, but it must be constant ly changed ; and that in every different part of her orb the will acquire different degrees of velocity; wherefore, to determine her true place at any given time, we must find the position of a right line, which palling through one of the foci




of the ellipsis, will cut off a trilineal area described by its motion, to which the whole area of the ellipfis shall have the same proportion that the periodical time of the earth has to any other given time which position being found, we thall have the place of the earth, at the given point of time.

This problem was first proposed by Kepler, after he had discovered the laws of uniform areas, and hence called by art has given in the paper before us. Several Mathematicians: have, however, solved it before Mr. Stewart, but not without. having recourse to the higher Geometry, or very operose methods of calculation, both which this Gentleman has avoided and solved the problem in an ealy, perspicuous, and strict geometrical method Art. 7 Of the Gold produced by evaporating Fluids, and of some

other means of producing Cold. By Dr. William Cullen, Profesor of Medicine in the University of Glascow.

From feveral experiments made by Dr. Cullen, it appears, that the power of evaporating Auids in producing cold, is nearly according to the degree of volatility in each ; and that the cold produced, is the effect of evaporation, t;

Art. 8. Contains experiments upon Magnesia, Quick-lime, and some other alcutlinie Jubitances. By Joseph Black,

M. D. This 'Gentleman's míotive for undertaking these experiments,

nents and cardia acknowlegement of his disappointment, appear truly laudable. My curiosity,' says he, «led me, "

lome time ago, to enquire more particularly into the nature of Mágnesia, and especially to compare its properties with those of the other absorbent earths; of which there plainly

appeared to me to be very different kinds, altho' commonly • confounded together under one name. I was, indeed, led to

this'examination, partly by the hope of discovering a new fort of lime, and lime-water, which might possibly be a more powerful solvent of the stone, than that commonly ufed'; but was disappointed in my expectations.'

The following process is given to prepare Magnesia. Dif< folve equal quantities of Epsom salt and of pearl ashes, sepa

rately, in a fufficient quantity of water purify each folu

tion from its dregs, and mix themi accurately together by * violent agitation: then make them juft to buil over a brifk 6 fire.

• Add now to the mixture three or four times its quantity of hot water; allow the Magnesia to settle to the bottom, and • "decant off as much of the water as posible. Pour on the Сс 2


' fame quantity of cold water; and after settling, decant it • off in the same manner. "Repeat this washing with the cold 6 water ten or twelve times; or even oftner, if the magnesia s be required perfectly pure for chemical experiments.

When it is sufficiently washed, the water may be strained • and squeezed from it in a linnen cloth; for very little of ( the magnefia passes through.”

. As a proof of the medicinal efficacy of magnefa, the Doctor informs us, that he made a neutral falt of magnesia and . distilled vinegar; chusing this acid, as being, like that in 6 weak stomachs, the product of fermentation. Six drachms of this being diffolved in water, was given to 'a middle-aged man, with directions to take it by degrees.

• After having "taken about a third, he defifted, and purged four times in ? an easy and gentle manner. A woman of a strong constitu«

tion got the remainder as a brisk purgative, and it operated

ten times, without causing any uneasiness. The taste of . this salt is not disagreeable, and it appears to be rather of the cooling, than of the acrid kind.'

From hence Dr. Black proceeds to an invekigation of the chemical properties of magnesią. His experiments to this purpofe are well planned, and seem to have been accurately conducted; but they are so nunierous, as to extend to upwards of fixty pages, and at the same time so mutually dependent on each other, that we must refer the inquisitive reader to the original. Art. 9. Of the Analysis and Uses of. Peat; by. Alexander

Lind, Efq; This is far from being one of the least important'articles in this collection: the particular design of it is, to render the fubject treated of more extensively useful. Besides the purposes for which it has been commonly employed, Mr. Lid conceives it might be advantageously used for smelting iron and other

The method 'he recommends is, ''to bring them to be as solid and compact a substance as poflible. The densest ** bodies,' he observes, cæteris paribus, when thoroughly I heated, are the hottest: hence it is, that metals, as they

are the heaviest bodies, so they reach the greateft degree of heat. The same holds in fewel; the hardest woods are made choice of when a strong heat is wanted; and even in commou peats I have shewn you how far preferable the hard and

solid are to the light and spungy. By fome experiments * which I have made, I find it to be no dificult matter to bring peat to a considerable degree of solidity, as you yourselves


[ocr errors]


may fee, by the specimen I now shew you. The simple

operation of grinding does the business; and as a peat, when < taken out of the moss, is a foft body, and easily grinded, a ( machine may be easily, contrived to grind, at a moderate

expence, several tons in a day. The charge of digging

peats, cutting them into squares, or the form of bricks, when • of a proper dryness, will be little different from that of mak• ing peats in the ordinary way. The folidity of peat prepar'sed in the manner mentioned, is surprizing; its specific gra

vity being somewhat greater than that of pit-coal.'

The advantages of peat-afhes and peat-duft, for manure, are pretty well known in South, as well as North Britain. But as this gentleman has propofed another method of using peat, for the melioration of land, what he has advanced on this fubject may prove a serviceable hint to such as have sandy farms, and are situated in the neighbourhood of this commodity.- Peatmoss,' he says, 'being wholly a vegetable matter, muft, if reduced • to a thorough state of putrefaction, answer the same purposes of « fertilizing ground, as other putrified vegetables. While it • lies in the moss, there is too great a quantity of water, to • raise a fufficient degree of heat, to bring the vegetables of « which peat-mofs is composed, whether actually growing, • decaying, or decayed, to a complete degree of putrefaction. < But if it were taken out of the moss, and laid in heaps, like • other vegetables, to rot, with a degree of moisture fuit« able for that purpose; and if, to begin, and also quicken, • the putrefaction, green, fresh, succulent plants were employ• ed in a sufficient quantity first to raise a heat; this I make ' no doubt would, by communicating it to the moffy sub• stance, in a suitable time, and by right management, reduce o the whole mass to the state desired.'

The mention of two other uses of peat concludes this article ; the one is, that peat-duft ftrewed upon ground where peas,

or other feeds are fown, in order to have an early crop, is an excellent preservative of such vegetables from the frost; as it keeps the ground warm. The other is, that there is nothing properer than peat to stop water, and to confine it, in the making of filh-ponds,' &c.

Art. 10. The Effects of Semen Hyosciami Albi, by Dr. Archibald

Hamilton, Pbysician in Edinburgh. The effects here described, are such as might naturally be expected from an over-dose of any narcotic vegetable: but what makes this case the more remarkable, is, that the patient


Сс 3

had accustomed himself to the use of white hen-bane feed, in order to procure sleep, for two years before, and that the iquantity at this time taken, did not exceed twenty-five grains. In'] Art. 11. The effects of the I horn-apple, by Dr. Abraham Swaine,

Physician at Brentford, ujarins In this case the framonium was gathered, and taken, instead of the fruit of the Burdock, which is said to have been advised as a remedy for the gravel. The consequence that happened is not near fo unaccountable, as that such a mistake could be made. It also is not impossible, that, the patient might further misunderstand his adviser, and look for fruit, instead of a root; the latter being a common prescription for complaints of that fort. Art. 12. The effect of Musk in curing the Gout in the Stomach;

by James Pringle, Esq; late Surgeon to the third régiment of foot-guards.

The case is thus related. A gentlewoman aged forty• three years, naturally of a delicate constitution, who has • been for several years subject to hylleric fits, attended with a

dry asthma, which her shape much contributed to; was fre« quently attacked, to a violent degree, with the gout in her • head and stomach, as well as in all her extremities and 6 with which she was lame the most part of Summer, 1745. « On the 3d of November following, fhe was violently seized « with it in her stomach, which occafioned violent hiccups and convulsions of the part. The description The

The description she gave of it was, « that as soon as these fits seized her, there came on a violent

working of her stomach, and so great an agitation of her « back, that her maid was not able to keep her hand on it. < By degrees it rofe to her throat'; when the was almost firan

gled. She could by no means lie down, but was forced to • fit night and day in an easy chairs and even then, if the cleaned her head to the one side or the other, it gavę

her « great pain, so that he was obliged to fit in an erect posture, - Her legs were very much swelled, which subfided a little on

laying them on a chair; but as soon as that happened, the ( asthma returned.'

In this condition Mr. Pringle found his patient on the 2ift of November; when he ordered her the following bolus ;

R Cinnab. natiu.

Antimom. ana. gr. XXV.
Mosch. opt. 77. xvi.
Syr, bal}. 2. %. F. Bolus,

[ocr errors]
« AnteriorContinuar »