than the ball of gold, though not so high as the ball of silver: and by making trials with different metals, he at length ascertained the quantity of alloy which the crown contained.

If, instead of marking the heights to which the masses of gold and silver raised the water on immersion, Archimedes had estimated their respective weights when immersed in water, he would have been able to have solved the problem with greater ease and exactness. For a solid immersed in a fluid loses a proportion of its weight equal to the weight of the quantity of fluid displaced. If a body be weighed in air, and then in water, the equilibrium of the balance is instantly destroyed on immersion. and the weight which restores the equilibrium is equal to the weight of a quantity of water of equal buik with the immersed solid. Thus, if a guinea weigh, in air, 129 grains, and if, on immersion, it requires 74 grains added to it to restore the equilibrium, this shows, that a quantity of water equal to the bulk of a guinea weighs 7 grains. Now had Archimedes weighed in water the crown and gold ball, which he found of equal weight in air, he would have found that on immersion, the one was heavier than the other. The pure

gold, not being equal in bulk to the mixture of which the crown was made, would have displaced a less quantity of water, and of course would have lost less of its weight than the crown; and it would thence have been apparent, that the crown had been alloyed with some metal of inferior value, and whose specific gravity was less than that of pure gold.

Specific gravities were formerly ascertained by an instrument called the hydrostatic balance, which dif!fered from the common balance only in being of very nice construction, and having a hook at the bottom of each scale, on which small weights might be hung by horse-hairs, silk threads. This instrument was improved, by appending to one end of the beam a glass ball for ascertaining the specific gravity of fluids, and a

BELFAST MAG, NO. IX.

or

glass bucket for ascertaining that of solids. But latterly the form of the instrument has been entirely changed, by the attempts of various ingenious men, to reach perfection. Of the several instruments which have been contrived, that of Mr. Nicholson, as improved by Mr. Laurie of Glasgow, appears to be the best. It is termed hydrometer, and can very conveniently be employed both for fluids and solids. The instrument at first consisted simply of a glass ball, to which a small rod, having a little bucket or cup for containing weights was fixed at top, and likewise a small cup for the same use at bottom. One defect of this instrument was, that it was readily. overset. Toremedy this inconvenience, Mr. Laurie added two bars, which extend to a considerable length below the body of the instrument, and which by bearing weights, in a small cup, at the lowest part, throw the center of gravity so low, that the instrument always remains in its proper position.

This will be better apprehended by a particular description.

the glass vessel, A, E, and has the glass ball B, connected with it, by the small metal rod a, c; d, is a small cup at the lower part of the frame, for containing weights; e, is another small cup, which is fastened to the glass ball, and which is used for the same purpose. The instrument is so constructed, that 1000 grains put into the cup d, shall bring down the glass ball B, till the rod a, c, be half immersed in the standard fluid-viz. distilled water, at the temperature of 60° Fahrenheit. The rod a, c, is graduated by experiments made for the purpose, so as to correspond with weights put into the cup d.

Let it be supposed now, that I want to know the specific gravity of any fluid. I pour a suflicient quantity of it into the vessel A, E, and mark the point of the rod a,c, where the fluid strikes, on the glass ball being immersed in it. This determines immediately the ratio of specific gravity between it and the standard fluid. Or, put into the cup d weights sufficient to bring the rod a, c, to the point at which it stands, when the standard fluid is employed-This determines the point as before. Suppose 900 grains produce this effect ;-The ratio is as 900 to 1000-That is the specific gravity of the fluid is 9 the standard fluid being taken as 1.

But let it be required to determine the specific gravity of any solid. Pour distilled water into the vessel A, E; take the weights out of the lower scale d, and put in the solid, whose specific gravity is required. Admit that the solid employed is not sufficient to bring the rod a, c, to the zero point, and that I find 100 grains additional are necessary to produce this effect: this determines that the absolute weight of the mass is 900 grains. Take now the substance out of the scale d, and put it into the scale e, it loses a part of its weight, which of course is the weight of a quantity of water of equal bulk. Put weights into the lower scale, to restore the equilibrium, then the proposition is" As the loss sustained is to the absolute weight, so is the specific gravity of the fluid to that of the solid."-Thus, a guinea

weighs in air 129 grains; it loses in water 7.25: therefore 7.25: 129 :: 1.000: 17.793, the specific gravity of gold. The meaning of which is, that a guinea is 17.793 times as heavy as its bulk of water.

By the hydrometer I can likewise ascertain the exact proportion of metals in any compound. Suppose I wish to determine how much alloy there is in a guinea, or what proportions of copper and pure gold there are in guinea-gold. By experiment, I find the specific gravity of guinea-gold to be 17.793, and I know, by the tables, that the specific gravity of fine gold is 19.637, and that of copper 8.843. I then subtract the specific gravity of copper from that of the compound, and the specific gravity of the compound from that of gold-The first remainder shows the bulk of gold, and the latter the bulk of copper, in the whole compound-These 1 multiply by the respective specific gravities, and the products show the proportion of weights of each metal in the compound.

from 17.793 specific gravity of compound, take 8.843 specific gravity of copper,

8.950 bulk of gold in the compound. and from 19.637 specific gravity of gold, take 17.793 specific gravity of compound, 1.844 bulk of copper in the compound. there 8.950 X 19.637 gives 175.75 proportion of gold,

and

1.844 8.843 gives 16.3 proportion of copper, Or 22 to 2 nearly.

Thus I find that in guinea-gold, for every 22 parts of pure gold there are 2 parts of copper. This experi ment may be extended to any compound metal; and thus it will be easy to determine, whether a suypected metal be genuine or counterfeit.

I shall conclude this paper by remarking, that though many persons may never have occasion to make experiments respecting specific gravties, yet it must be pleasant for all to know something of the subject An acquaintance with the general doctrine will frequently be found serviceable in reading and in conversation. At all events, inquiries of this nature form a pleasing and useful exercise for the powers of the human mind. A. Z.

1809.]

WE

E have been favoured with the sight of a letter from an officer in Portugal to his relations in this country, and been permitted to make the following interesting extracts from it. We doubt not but it will prove acceptable to our readers, as it conveys the information in so neat and lively a manner.

Lumiera, March 2, 1809. "I had a long spell of the complaints which are so prevalent in this country, and you will not wonder at my being ina particularly good humour, when you hear that I am at this moment sitting, enjoying as a convalescent, one of the loveliest days you can conceive; my room full of geraniums, in full blossomi; woodbine, carnations, &c; as delightful a view as you could wish of the whole country, full of orange groves in blossom, olive plantations, vineyards, &c. Could I convey, by a wish, those I wish for, and place them beside me, I should have nothing left to desire, and I can assure you that my thoughts are oftener turned on the fire-side of home, than perhaps a soldier's ought. We remain here in as much tranquillity, and hear the different reports of the advance of the French with as much composure as if it were none of our business to oppose them; however, we have now some likelihood of advancing; our baggage is agam curtailed; mules ordered to be provided immediately, and I hope that a very few days will see us in motion. Our route this time will be different, which I am glad of, as it will give us an opportunity of seeing more of the country. A march now will be delightful, the weather is as warm as in July, and the spring very far advanced. I fancy there is no doubt that the French are advancing three columns, making in all thirty or torty thousand men, a number we shall be more than a match for, as General Sherbrooke has brought a reinforcement, and we have now upwards of twenty thousand English in Portugal. The whole army, with the exception of a few regiments who garrison Lisbon, are in cantoniments, ten or twelve miles distance from it. Did I tell you that I had been at that sweet place Cintra, where I passed two days with a very pleasant party, rambling about, and seeing all the Moorish and Roman an

275

tiquities, with some very ancient con vents? One of the latter which is perched on the very top of the highest rock in Lisbon, has a very beautiful altar of alabaster, which contains (in what I believe you call al-fresco) the whole history of our Saviour's sufferings, and some of his principal actions. The priest who showed it to us, put a light behind it, and it was as transparent as glass. I also went to see the palace of Calouse, one of the Prince Regent's most favourite seats, and a most magnificent one it is. Will you believe me when I assure you, that for more than a mile and a half on the high road it is bordered with geraniums, roses and myrtles; and in the beginning of February when I went there, those flowers were in full bloom. Two officers joined us a few days since, from the 1st battalion, which is in Malta; they complain of Malta as very stupid quarters, on account of the season, which is Lent, and nothing going forward but prayers, a kind of pastime, which, as my correspondent expresses himself, the heroes in red have but little esprit for. With us, or at least while we were in Lisbon, it was much the same. Religious processions superseded operas, and inost ridiculous things they are. Fancy some hundred of the fat race of people here, employed in carrying images of all the saints in the calendar, all of them, but the females especially, dressed out in the most tawdry style, as large as life; and faith no small burden to the carriers, who labour most piteously under the load. This show is attended by crowds of nobility and gentry of both sexes, all marching in procession through the principal streets, and what is really wed worth seeing, is the number of very beautiful women, who show themselves at the windows, and in the balconies, elegantly dressed, and who kneel down as the host, or the images of their favourite saints pass. I have been but at few parties first, from illness, and now I am ashained to go, as an enormous Portugueze wig, decorates or rather disfigures my poor nob, which I was obliged to shave after my long continement, as my hair was tumbling off. I often think what a prize my head, or at least the cover◄ ing of it will be to some bald Frenchman, who may chance to knock it off.

1 hope to write a more interesting

letter from the frontiers. The good people here do not seem quite as secure of our triumph over the French, as we vain fellows do; at least, they are taking prudent precautions to ensure a retreat to the Brazils.

"I had contracted an intimacy with a very learned and gentleman-like French professor, at the Convent of St. Vincent's (one of the finest, by the bye, in Portugal) they have a very elegant library, immensely large, and full of the rarest and most valuable books, where I used to pass many a pleasant hour. What was my surprise on going there one day, after a fortnight's absence, while I was ill, to find every thing packed up, and ready to send aboard a ship, those prudent monks had hired to convey them at a moment's warning to the Brazils. It is the same in every private and public place. Every thing of value is removed, or ready to be so. 1 think that for this once if the French do beat us (which in my humble opinion

the last time fought and conquered the united foes of his country. But, he fell in the meridian of his fame, and one moment made him immortal in both worlds.

"His career of services had been long, but it was in the middle of the last war that he burst upon the public eye as a luminary of the first magnitude.

"At the battle of Aboukir, he rose like the sun in the east, and like the sun too, after a summer's day of glory, he set in the west at the battle of Trafalgar, leaving the ocean in a blaze as he went down, and in darkness when he had descended.

"In ages to come, when the stranger who visits this island, shall inquire for the monument of Nelson, the answer will be-"Behold his country which he saved."

To the Editor of the Belfast Magazine.

SIR,

ERMIT me to reply to "Far

plundering in Portugal. The chapels are already pretty well stript, and all the principal merchants are prepared to set off at a moment's warning.

"You have no doubt heard, that General Beresford is made field marshal here to instruct and organize the Portugueze troops. I shall take the liberty of sending you what I hope you have not before read, and what is in my opinion a very beautiful extract on the death of Lord Nelson. I know my father and mother will read it with great pleasure, a thought that gives mę no small degree of the same sensation."

"ON LORD NELSON'S DEATH. "Still it is impossible to reflect upon the great victory which that gallant hero purchased for us with his life, without feeling a mixed emotion of joy and sorrow, of mourning and triumph. The glory and the calamity, like the angels of Mercy and Affliction travelled toge

ther.

"At what period was that victory achieved! how seasonable! how well tuned! Whilst on the Continent, a wretched and incapable general,* had without a battle, surrendered himself alive into the hands of Buonaparte, our English hero, once more, and for

* General Mack.

March 1809, page 193, No. 8) That

writer says, the statement is fairly made on one acre in the drill, or rather bank-mode, and one acre in the lazybed way." Now I contend this is not the case; let the reader determine. The charges on one acre in the drill way, are stated at 3l. 8s. 11d. (includ ing forty loads of dung, 21. 3s. 4d.) The charges on one acre in the lazybed mode, are stated at 23. 13s. 4d. (including three hundred and twenty loads of dung, 171. 6s. 8d.) Is there not in the latter case, charged for dung eight times the sum, and quantity charged for it in the former? To have made the comparison "fair," the dung for each process should have been alike in quality and expense, unless it be true, that in order to raise a lazy-bed crop of potatoes, exceeding a drilled one, only two barrels, eight times the dung and seed be required; also, that more than seven times the expense in labour is requisite, and that the benefit to the succeeding crops is equal. Whatever may be the opinion on the quantity and expense of dung, seed, and labour, requisite for each process; it will not be contended, I presume, that forty loads of dung will be as beneficial to the succeeding crops as three hundred and twenty loads; the excess ought to

go to the credit of that process, to which the greater quantity was applied. There is another circumstance which makes the statement in question not fairly comparable; viz. that as the ploughing and harrowing of the drill crop are not charged, because, "they would be given the land had it been a fallow;" for the same reason, the lazy bed mode should have been charged only with whatever expense was bestowed on it in labour for the potatoes, more than would have been bestowed had it been a fallow. How the Farmer could make such a mistake as to unagine that the last statement was a fair one tor one acre, I am at a loss to conjecture; perhaps it arose from his taking it for granted that it was so, because the author expressly says "he has given it for one acre only;" I also might have been deceived by this assertion, had I not observed in the next lines, the words, "here we have eight acres highly dressed for a subsequent crop." It is true, he says, "with the same quantity of dung as the one acre," it is, however, a fact, that he has charged eight times the quantity." Certainly, no person who is acquainted with the expense of planting potatoes with the spade, can think that eight acres could be done in that way for 21. 3s. 4d. I am in doubt whether one acre be done generally for that sum, indeed I am inclined to think the expenses on the drill method are also underrated. You have the "Farmer's," and my opinion on anonymous communications, and you will, I have no doubt, "know what value to set upon them," and while I acknowledge that, "the value of communications ought to be estimated by the importance of the subjects, and the soundness of the reasoning employed, and not by the name of the author," I hope I may be allowed

to entertain the opinion that, unimportant subjects, and unsound reasoning are more likely to come from the anonymous writer, than from him who gives his name; for this plain reason, that the latter will be more wary, as he may lose his reputation as well as have his feelings wounded, while the former can sustain only one of those mortifications. On subjects of agriculture, the name and place of abode of a writer are particularly useful, the farmer who is about adopting any system recommended, wants to be satisfied in a thousand particulars, which the author may not have noticed; many of your readers who would ride miles for such information, would not put pen to paper to obtain it; more value would be set on five minutes' conversation with the person recommending any system, than on volumes of book-information; in saying this I take it for granted" book-farming" is esteemed in this country, as little as it is in England. Although "The Farmer's Magazine, principally composed of anonymous pieces, is held in great estimation, and has materially served the cause of agriculture," it does not follow that it would not have been in higher estimation, and have still more served the cause of agriculture, had it not contained so many anonymous communications. Lest the "Farmer" should fancy I am a favourer of the lazy-bed mode, in preference to the drill one, I assure him I am not; it will not be easy to bring an Englishman to prefer the former, at least if profit be his object; but I find the prevailing opinion is, that if the palate only be consulted; the lazy-bed mode should be practised. I am Sir, your, obedient servant, WM. GOOCH. Castie-Upton, April 1809.