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to silk by simple immersion, without the aid of acids.

Richard Walker, Esq. of Oxford, has proposed an alteration in the scale of the thermometer, which suggested itself to him during a long course of experiments, and which has been adopted by himself and his friends from the persuasion of its being founded on the truest principles." The two fixed points, the freezing and boiling points of water as they have hitherto been, will (he observes) probably never fail to be continued, as being perfectly sufficient for the accurate adjustment of thermometers. The commencement of the scale, and the number of divisions, only appear to claim attention. With respect to the first, since neither the extremes of heat or cold are likely to be ascertained, the hope of fixing O at either of these may be entirely relinquished, and it remains to fix it at the fittest intermediate point. Here I propose the following mode of graduation: Having ascertained that the temperature of 62° of Fahrenheit is the temperature at which the human body in health is conscious of no inconvenience from heat or cold, and that a deviation from that point of only one or two degrees, above or below, actually produces that effect under ordinary circumstances, I fixed my zero or O there. I adopted the divisions of Fahrenheit, considering those of Reaumur, the centigrades, &c. as too few, and decimal divisions unnecessary. Hence it will follow that O being placed at 62° of Fahrenheit, 150° will be the boiling, and minus 30°, the freezing point of water, and all other points on Fahrenheit's scale may be reduced to this, by subtracting 62 for any degree above O of Fahrenheit, and adding 62 for any degree below 0. For ordinary meteorological purposes, a scale of this kind extending to 65° above, and as many below 0, will be sufficient."

It has been found that camphor mixed with different fixed oils and sand,

in order to divide the particles, may be purified of its oily particles, and deprived of its empyreumatic smell, when sublimed with a small quantity of potash. The process by which this effect is produced, is described as follows: Two drachms of camphor, with considerable empyreumatic smell, and dirty, were mixed with one of olive oil, and eight of sand; after which twenty grains of pure potash were added and heat applied; but though it was greater than is necessary for its sublimation, the product was perfectly free from empyruematic smell, and a little whiter than it generally is. The substitution of linseed oil produced no alteration in the product, The subcarbonate does not answer the purpose, because in that state the affinity of potash for oils is less than when entirely deprived of carbonic acid.

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*Where Dr Jenny, it is believed, was Rector. He resided in the neigh, introduced into Swift's poem on Hamilbourhood of Sir Arthur Acheson, and is ton's Bawn. See Swift's Works, 1808, vol. xvii. p. 9. This perfectly characteristic Letter, which has been among the desiderata of all former editions, is now first printed by the favour of Lord Viscount Cremorne, in whose family it been, many years ago, noticed by Dr has been preserved. The letter had Thomas Campbell, an Irish clergyman, in his Philosophical Survey of the South of Ireland." N.

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great ingratitude and breach of hospitality in publishing a copy of verses †, called HAMILTON'S BAwn.The writer hath likewise taken severe notice of some other verses published many years ago by the indiscretion of a friend, to whom they were sent in a letter. It was called a JOURNAL, and writ at Mr Rochfort's ; and the consequences drawn from both by this late writer is, that the better I am used in any family, the more I abuse them; with other reflections that must follow from such a principle. I was originally as unwilling to be libelled as the nicest man can be, but having been used to such treatment ever since I unhappily began to be known, I am now grown hardened; and while the friends I have left will continue to use me with any kindness, I shall need but a small degree of philosophy to bear me up against those who are pleased to be my enemies on the score of party-zeal, and the hopes of turning that zeal to account. One thing, I confess, would still touch me to the quick; I mean if any person of true genius would employ his pen gainst me; but if I am not very partial to myself, I cannot remember, that among at least two thousand papers, full of groundless reflections against me, hundreds of which I have seen, and heard of more, I ever saw any one production that the meanest writer could have cause to be proud of; for which I can assign a very natural reason; that during the whole busy time of my life, the men of wit (in England) were all my particular friends, although many of them differed from me in opinions of public

+ These verses were written in 1729. See them in vol. xvii. p. 85. See also, in vol. xvi. p. 444, the Dean's Poem in 1728," On cutting down the old Thorn

at Market-hill." N.

At Gaulstown, in the county of Westmeath, in the year 1721. See vol. xvi, pp. 251-2, 182. N.

persons and proceedings. As to Ire land, where I lived very little before the Queen's death, and ever since in perfect retirement, I remember to have published nothing but what is called the Drapier's Letters, and some few other trifles relating to the affairs of this miserable and ruined kingdom. What other things fell from me, (chiefly in verse,) were only amusements in hours of sickness or leisure, or in private families, to divert ourselves and some neighbours, but were never intended for public view; which is plain from the subjects, and the careless way of handling them: neither, indeed, can it answer the true ends of vanity or desire of praise, to let the world see such little sallies of fancy or humour, because if they be ill or indifferently performed, (which must often be the case,) the loss of reputation is certain; and however well executed, after a week's vogue, they are utterly forgot. I know not how I come to be led so far from the subject of your letter.I confess there were some few persons who made random conjectures that you might possibly be concerned in the paper you hint at, but they were such who knew very little of you or me; for others, who were better acquainted with us both, have always cleared you, because they did not. look upon that paper any way equal to your known good sense and candour, or talent of writing. And as to myself, I had further conviction, because I knew how well you were acquainted with the whole history and occasion of writing those verses on the Barrack; how well pleased the master and lady of the family were with it; that you had read it more than once; that it was no secret to any neighbour, nor any reserve but that against giving dents that reserve was broken by granta copy. You know well by what inciing a copy to a great person, and from thence how it fell into other hands, and so came (as it is the constant case)

to be published, and is now forgot. I confess my own conjectures about this late libel against me lay towards another gentleman, who, I am informed, hath since cleared himself, I mean Dr Tisdall*; but that suspicion was first taught me by others; and yet I know very well, that for at least fifteen years past, he hath been often engaged in a kind of flirting war of satiric burlesque verse with certain wags both in town and country, who, it seems, were provoked with his faculty of jibing, and used to answer him in his own way. Yet I have been ase sured, that in these combats he was generally mistaken in his adversaries, falling foul upon many persons who never dipt a pen either for or against him; and I think you, among others, had some marks of his favour. But, as to me, who, I solemnly profess, was always entirely innocent, during the whole time that his pen and tongue took this unhappy turn, as well as be fore and since, I could never be one month at peace for his wit; whatever was writ to ridicule him was laid at my door, and only by himself; with a further declaration, much to my honour, that he knew my stile, would trouble himself to inquire no farther; and, using my surname, said, I was his man. Some of his performances I have seen, and have heard of more, besides the great number he kept in petto; so that five or six gentlemen have often and very lately assured me, that in one evening sitting he has produced a dozen of his libels wholly against me; desiring I might be told of it, and assuring those gentlemen

*To this gentleman Dr Swift addres sed a letter, April 20. 1704, on the subject of his addresses to Mrs Johnson; assuring him very candidly, that he had himself never seen any other lady whose conversation he entirely valued; and freely giving consent to her marrying Dr Tisdall. See vol. x. pp. 33, 41. N.

that the whole dozen should be published if I would not let him alone. This was a little hard upon me, who had never one single moment in my life the least inclination to enter the lists with him, at those or any other weapons whatsoever, any more than I would venture to sit four hours. disputing with him any point of controversy. I confess, this keenness of the Doctor in determining, whenever he was attacked, to fix on me for his adversary, inclined me to conceive that he might have probably writ this last paper, and other people had the same thought; but I hear he hath utterly denied it; and I believe him; for I am confident he is an honest man, but unhappily misled through the whole course of his life, by mistaking his talent, which he hath, against nature, applied to wit, and raillery, and rhyming: besides which, his incurable absence of mind, on all occasions, and in all companies, hath led him into ten thousand errors, especially of that kind, which are mortal to all agreeable or improving conversation, and which hath put him upon such a foot with every friend, that I heartily lament the situation he is in.

I intreat your pardon for the length and insignificancy of this letter, but my solitary way of life is apt to make me talkative upon paper. I desire you would believe, first, that I have so frequently been libelled, that my curiosity to know the authors is quite extinct, though that of some friends is not; secondly, that I am not hasty in judging men's stile, or matter, or malice. I can venture to say, that a thing is not written by such a person, because it is much below his good sense; and to look among the herd of dunces is endless. As to yourself, I hope you will be my witness, that I have always treated you with particular distinction; and if we differ in opinions relating to public proceedings, it is for very good reasons: you are an expectant from the world and from

power;

power; I have long done with both; having been an original offender against all principles set up since the death of the Queen, I could not think it worth my while to quit my old ones*, and must have done it with an ill grace, though honour and conscience had been out of the question. Whoever really believes that things are well, is many ways happy; he is pleased with the world, (as I was formerly,) and the world with him; his merit is allowed, and favour will certainly follow; which I heartily wish you; only desiring, that in what appears to my eyes a very dirty road, you would pick out the cleanest stages you can; and believe me to be, with much esteem,

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The columns vary, in imperfect forms, from the trihedral to the heptaedral: some diminish towards their points, and end in obtuse faces; others, on the contrary, preserve an equal diameter. Many of them are scattered in masses, or insulated, and of various dimensions. The largest which I saw on the Kschoes, was 87 feet in height and 324 in diameter. When these columnar-formed rocks constitute the summit of the ridge, their direction is perfectly perpendicular; as ex. gr. the Crown Mountain, north of Steppan Zminda; but if they are in large masses, or rise insulated above the mountains, they incline westward under an angle of 19o.

The substance of which they are composed is a coarse basalt, containing blackish-green schoerl; and whereever they have been rent by the cold of the accumulated ice, or by some other power, the fracture appears undulated. When the columns project beyond the top of the ridge, they are separated, and connected by a basis of compact, dark yellowish-grey schistus, of metallic splendour, and smooth to the touch, but in some places exfoliated and decayed. It fills up all the interstices and fissures, and strongly adheres to the rough basalt. But as soon as this schistus begins to sink into large, rough masses, it changes colour, becomes of a brilliant black, and indurated to a great degree.

It is only on the S.S.E. side of Caucasus that this substance is attach

At the highest summit, particularly on the western side, we commonly find a coarse kind of rock, interspersed with grey and black spots. In some parts, this continues to a great distance: in others, the masses are more accumulated and detached, and have a co-ed to the basaltic summit, which, after lumnar-form cohesion. Single columns, likewise, project high above the flat back of the ridge, and are generally covered with snow, or clouds.

* When he quitted the Whigs, he thought it worth while to quit still older principles. See his Letter to Stella, Sept. 9. 1720, where he mentions Lord Godolphin's receiving him coldly, and says, he will make him sorry for it.Vol. xiv. p. 220. N.

a fall of 229 feet, lays on the coarse, grey rock: but to the S. E. and E. it is incumbent on granite, it is even visible at the foot of the mountains, and forms there peculiar rocks of some height.

I saw, in the island of Paros, a siasbestiform schistus, containing rough milar dark yellowish-grey, micaceous, garnets, incumbent on granite, and laying under marble.

Besides the uncommon hardness of the

the schistus, it is strongly impregnated with yellow mica: cubes of marcasite are also found in great abundance, in the lower soft strata, partly uncovered, and partly in spathose quarz. Hence, in fine, clear weather, the mountaineer sees his black mountains glittering like gold; and often bitterly laments, that he does not understand the art of reaping those fruits which his country apparently offers.

It appears as if this schistus had covered formerly the whole south-eastern surface of Caucasus; for I have seen it laying on different parts of the principal mountains, and filling up the largest clefts. The uppermost beds are very hard, yet it is always found in larger or smaller fragments; but when it fills up the lower clefts, it is softer, and exfoliates into plates, or flakes, from the thickness of some feet down to an inch. Plates, from one to two inches thick, are used by the civilized mountaineers for the purpose of baking their bread; but if they incautiously heat them red hot, the plates fly into innumerable pieces, frequently to the injury of the by-standers.When they find any long round pieces in the streams or rivers, they employ them as pestles, but the softer kind serves the gold and silver smiths for touchstones.

We find another kind of stone, that contains neither streaks nor stratification, but only a separation of its component parts. It is generally a grey, or white and brown speckled, smooth granite, undulated on the exterior surface; but in many places it occurs of different degrees of hardness, and brilliancy of colours. Granite, in some lower parts, certainly constitutes the summit of Caucasus, but it does not run deep; though it should seem as if the middle mountains were really incumbent on it, for it frequently appears between them, and but seldom in the promontories. We might immediately conclude, with a certain degree of reason, that granite was the most ancient

species of all Caucasus, but in the sequel I shall bring proofs to the contrary; and I think I may venture to assert, that even the origin of this granite was the work of an earlier, not less strong operating, power of nature, underlaid by another species of stone still to be met with in the mountains.

Most of the fissures of the compact granite are filled with the finest white quarz; and the largest and hollowest contain beautiful crystals, whose bases generally adhere to the upper side, so that their points are free, and turned downwards more or less perpendicularly. The fissures also are commonly full of an unctuous yellow ochre, for the granite every where is moistened by the dropping of the water.

The clearest and most beautiful crystals are found in the rents or interstices of the highest columnar-formed rocks, under the snow; and in summer they often fall down with fragments of stone and ice. I have seen some perfectly black, others hyacinthine, but in general they are white. Their thickness is from two lines, to two, four, and six inches; the greatest length was rather more than ten inches.

However, I have been assured, that a hyacinthine crystal, completely transparent, preserved in the church at Steppand-Zminda, is eighteen inches in diameter, and 27 in length. Frequently, on the southern side of the mountains, masses of different kinds of earth and stones are incumbent on the above-mentioned granite. They appear partly under the form of a blueish white, or dark red schistus, and partly of a brown, basaltic, columnarformed granite.

All the preceding substances constitute the shell, or exterior stratum, of the primitive chain of Caucasus. The outer course of mountains are of another composition. Notwithstanding their great elevation, they bear marks of a more recent origin, and show that they were produced by other powers

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