Some Account of the Plan of Sauffure's Hygrometer. HG GREN THE it, by boiling in an alkaline lixivi- D e When these hairs were adapted to the hygrometer, which, like the ufual inftruments of this kind, fhows the changes in their length by the motion of a needle on a circle or a quadrant, it was neceffary to fix the extreme points of drynefs and moifture. M. Sauffure first endeavoured to afcertain the latter. He put the inftrument in a receiver on a plate whofe furface was covered with water, and frequently moiftened the anterior furface of the In this fituation the balancing weight ftretches the hair fufficiently; for, after being in the lixivium, it is fometimes a little curled. In this, ftate, in fome inftances, it continues to extend during a period of more than fix hours; in others, after extending to a certain point, it seems again to fhorten: thefe are proofs that its organization has been injured in the operation, or that, in the firft inftance, the weight is great. If a change in the weight too does Efais fur Hygrometrie. Par Horace. Benedict de Sauffure, Profeffeur de Philofophie a Geneve. 8vo. Neufchatel. Account of the Plan of Sauffure's Hygrometer. does not alter this tendency, it is rejected. If, after elongating, it retracts during its itay in the moist air, it is equally unfit for its purpofe. If at the end of two or three hours it becomes ftationary, and, after alternately removing it into a drier, and again into the moift air, it points to the fame degree, it is generally confidered as good. Warm vapour has no more effect than cold: though, in this obfervation, we believe our author differs from Dr Robinson, who, on trying the relaxing power of different fluids on the animal folid, and the kind of folid which he ufed was human hair, found warm water had the greatest power, and next to it cold water. This is an important fact, which cannot be too exactly afcertained. In thefe experiments, it is not pretended that the moisture of the air is as great as it will admit of: it is fufficient that it is a conftant and uniform degree; and this M. Sauffure has found, after a very careful examination. It is probable, indeed, that it is very nearly the greatest that the air will admit of, fince, even in the momentary in terval in which the hygrometer is expofed that the internal furface may be moistened, the needle begins to move towards drynefs. In different ftates of the air there may be fome variation; but the needle fhows no fenfible difference, on repeating the experiment at different times; and we may therefore conclude that it is conftant, particularly as the extreme moisture of the air in a natural ftate is fomewhat diftant from this artificial dampnefs, We may now add alfo, that the expanfion of the air is probably uniform, as different hygrometers, made with care, correfpond in different parts of the fcale. To determine e the extreme point of drynefs was a more difficult task. In this attempt, it is more probable ་ 223 that our author approximates only to it. His inftrument must be cart ried to the coaft of Guinea, and exposed to the harmattan to afcertain it. He mentions, that his extreme point, if it does not fhow that all the moisture which the air holds in folution for that which it contains, as an integrant part, must not be reckoned: but if all the additional moifture is not extracted, ftill the air is rendered drier than it ever appears when confined. Those, however, who have experienced the extreme drynefs of the wind we have juft mentioned, or even read of its effects, will wish that the experiment had been tried before the conclufion had been fo pofitively drawn. The common drynefs of the air seldom moves the needle beyond the twenty-fifth degree. Our author's method of drying the air, was to cover a plate of iron, rolled into a demi-cylinder, and heated to a red heat, with a powder compofed of equal parts of nitre and crude tartar. A detonation enfues, and the iron is in confequence of it covered with a cauftic alkali. This is melted, and calcined in a heat gradually increafing, that it may not be too fluid, for an hour. As foon as it is cold enough not to endanger breaking the receiver, it is put into it with the hygrometer and a thermometer, while the external air is carefully excluded. In this ftate. it remains fome days; if the inftru ment inclofed in the receiver is then put out into a warm fun, and any moisture fhould remain in the air, which the falt cannot attract from it, the moifture will be depofited, and in that feparate flate the alkali abforbs it. If the hair was properly dried, the alteration which the fun produces will not be oberved after the inftrument has been brought into a mean temperatures If the hair, fhut up with the alkali, fhews a tendency to lengthen with cold 1 cold, and contract with heat, and this tendency continues fome days, it is a proof that the inftrument is defective. Concentrated oil of vitriol, and terra foliata tartari, do not fhow fo great a power of attracting moisture from the air, as the calcined alkali. heat dilates the hair, according to the fame law, through the whole fcale. The variations are inconfiderable, except in very nice expe- . riments; and, in auother effay, the author fhows what allowance is to be made for them. About the fifth degree of M. Sauffure's fcale, the needle is ftationary on increasing the heat: the changes in the pyrometer are equal, and opposed to the changes of the hygrometer. We have hinted, that the inftrument, when made with hair, as a pyrometer, has a different and oppofite fcale to that which it must have as an hygrometer. Our au- As we have often spoken of the thor examines it with this view. author's fcale, we must here ob On examination, he finds, that a ferve that it begins at ọ, which is the degree of heat produces a change period of extreme dryness, and con equal to of a degree of the hy-fifts of 100 degrees; and the Loodth grometrical scale, if we fuppofe that is the period of extreme humidity. Letter to the Secretary of the Society for Encouragement of Arts, Manufactures, and Commerce *. SIR, WAS extremely fortunate, when As I must ever confider myself greatly indebted to the Society for the many honours received from them, fhould you approve of the difcovery being mentioned to the Society, and they think it worthy their attention, I fhall be extremely happy in giving them a particu lar account of the manner in which I accomplished my undertaking. I am, SIR, Your most humble fervant, at Florence the Summer before the laft, in the acquaintance of an Amateur of painting, who procured me the fatisfaction of feeing fome paintings in the ancient Grecian ityle, executed by Signora Parenti, a profeffor at that place, who received her inftructions from a Jefuit at Pavia, the perfon who made the fartheft difcoveries in that art. My friend, knowing I was fond of painting, very politely informed me what were the materials the Pain- Nov. 14. 1786. trefs ufed, but could not tell me the proportions of the compofition; however, from my anxiety to fucceed in fuch an acquifition, I made various experiments, and at laft obtained fuch a fufficient knowledge of the quantities of the different ingredients, as to begin and finifh a picture, which I fhall be happy to Jay before the Society for their infpection. METHOD. TAKE an ounce of white wax, and the fame weight of gum mattic in lachrymæ, that is, as it comes from the tree, which muft be reduced to a coarse powder. Put the wax in a glazed earthen veffel over a very flow fire, and when it is quite diffolved, ftrew in the maftic, a little at a time, ftirring the • Tranfactions of Society for encouragement of Arts, Manufactures, and Cqm-' metoe, vol. V. Remarkable Effect produced by the Representation of a Tragedy. 225 the wax continually until the whole, quantity of gum is perfectly melted and incorporated; then throw the paste into cold water, and when it is hard, take it out of the water, wipe it dry, and beat it in one of Mr. Wedgwood's mortars, obferving to pound it at firft in a linen cloth, to absorb fome drops of water that will remain in the pafte, and would prevent the poffibility of reducing it to a powder, which must be fo fine as to pass through a thick gauze. It fhould be pounded in a cold place, and but a little while at a time, as after long beating the friction will in a degree foften the wax and gum, and inftead of their becoming a powder they will return to a paste. Make some strong Gum-Arabic water, and when you paint, take a little of the powder, fome colour, and mix them together with the gum-water. Light colours require but a fmall quantity of the powder, but more of it must be put in proportion to the body and darkness of the colours and to black, there fhould be almost as much of the powder as colour. no more than can be ufed before they grow dry, paint with fair water, as is practifed in painting with water colours, a ground on the wood being firft painted of fome proper colour prepared in the fame manner as is defcribed for the picture: walnut-tree, and oak are the forts of wood commonly made use of in Italy for this purpose. The painting thould be very highly finithed, otherwife, when varnished, the tints will not appear united. When the painting is quite dry, with rather a hard brufh, paffing it one way, varnish it with white wax, which is put into an earthen veffel, and kept mehed over a very flow fire till the picture is varnished, taking great care the wax does not boil. Afterwards hold the picture before a fire, near enough to melt the wax, but not make it run; and when the varnish is entirely cold and hard, rub it gently with a linen cloth. Should the varnifh blifter, warm the picture again very flowly, and the bubbles will fubfide. When the picture is dirty, it need only be washed with cold wa Having mixed the colours, and ter. Remarkable Effect produced by the Reprefentation of a Tragedy in Germany. M. SCHILLER, whofe Tragedy of The Robbers had extraordinary fuccefs on all the German theatres where the reprefentation of it was permitted, is none of thofe people that, like fafhionable fongs, are praifed by all the world for a time, however defpicable their merit may be. He is a young writer, who feems made to aftonish the age, fome time or other, with the vigour of his genius. His fortunes will be diligently attended to by every perfon of tafte. VOL. VI. N° 34• His pieces, taken together, and even the feparate fcenes of them, are in the very worst tafte; but the fublime ftrokes they abound with, and efpecially a horrible kind of intereft, that, in fpite of ourselves we are obliged to take in them, attaches us to feenes to the last degree terrifying. The Count de Moor, an unfortunate youth, abandoned by villains to the remorfe that ever accompånies guilt, terrible, like Achilles in *__ his rage, vows to avenge the inno E e cent 226 Remarkable Effect produced by the Representation of a Tragedy. cent on the wretches that opprefs them. He is made chief of a band of robbers. His character is marked with fo much force and dignity, that when the piece was reprefented at Fribourg in Brifgaw, it made a dreadful impreffion on the youth of the place. Whatever opinions may be broached by the fpeculatift, it is certain that virtue is never attained by guilty means; but fuch is the effect of a paradox fpeciously decked out, that a great number of these young people, the flower of the nobility, and most of them ftill at college, refolved to form a troop like that of Moor, to affume to themselves the character of exterminating angels; and in the happy age of friendfhip, love, and heroifm, to unite themselves by oaths almost as dreadful as thofe of Cataline. The young Count of S-, of one of the most ancient German families, was named chief of the troop. Each was to poffefs himfelf of all the money and jewels which he could lay his hands on in his father's house. It was alfo projected, that they fhould carry off Mifs a lady of great beauty and illuftrious family. This was to be done on the public walk, with arms in their hands, after which they were to retire into the woods. The fatal hour, when this dread. ful confpiracy was to be put in execu. tion, was almost at hand. It was fixed for the afternoon of a holiday. On that very day, the Principal of the college received an invitation to a party of pleasure in the country on the morrow, and he iminediately propofed to the young folks to defer their holiday till then. They could not refufe, and the Principal retired to his chamber, where he found a note fignifying that the party he had been invited to was not to take place: he immediately returned to acquaint the lads, if they were not already gone, that they might take their diverfion that afternoon. He found the door of the school fhut, and heard a fort of agitation and whifpering that alarmed him. He knocked, it was fome time before they opened; and while he afked the reason, and they were expreffing their surprise at his return, and endeavouring to amufe him with feigned excufes, he perceived that many of them were concealing papers. Luckily, as he turned round, he faw behind him one of thofe papers lying on a bench, and fo contrived it, that, without their observation, he stept back a little and fat down on the paper. He then chatted with them about fome indifferent things, and difmiffed them. But what was his furprize, when he found a full account of the plot, a lift of the confpirators, and the execrable engagements, figned with their blood, that each had come under. Not knowing on what to refolve in fuch a cafe, he hastens to the governor of the town, who immediately sent to all the parents the ftricteft injunctions to fecure their children inftantly, otherwife he would make themselves answerable if they escaped. As it was a mere fit of temporary infanity that gave rife to this horrible plot, it was not thought expedient to require the interpofition of the laws, but the young confpirators were inftantly feparated and difperfed among fuch regiments as were the most strictly dif ciplined. And the tragedy was prohibited ever afterwards at Fribourg, and in feveral other of the towns in Germany. Such terrible effects prove the amazing energy of M. Schiller's pen. This gentleman, it would feem, has been obliged to quit his native city Wurtemberg. He now refides at |