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A very different resulc attended the Author's next experiment-apparently in consequence only of his having introduced into the receiver, through an aperture in the top of it, a piece of the oiled leather abovementioned. On working the pump ten minutes as before, the 'barometer gage marked a degree of exhaustion equal only to 300; but the pear gage indicated a degree of rarefaction not less than 4000.
On removing the oiled leather, and again working the pump, the two gages agreed perfectly, as before.
That he might, as it were, analyse the leather, or discover to what principle contained in it this aftonishing variety was owing; the Author separately and successively included in the receiver two ounces of tallow; the same quantity of oil; and of allum; and a piece of leather in the state in which it is received from the leather-sellers, With the three first of these substances included in the receiver the exhaustion did not exceed 600, as indicated by either of the gages: but when the leather alone was put into it, the difference in the testimony of the two gages was very remarkable. The elastic vapour fupposed to proceed from it supplied the place of the exhausted air so very fast, that the barometer gage, after ten minutes work. ing of the pump, could not be brought to indicate a degree of exhaustion greater than 159; whereas the pear gage indicated a degree of rarefaction that was estimated at one hundred thoufand.
To determine whether this enormous variation in the testimonies of the two gages proceeded from moisture in the leather, the Author repeated the experiment with a piece of fresh leather that weighed 100 grains. The pear gage, as before, indicated a rarefaction of 100,000. The fame piece of leather being tried again, after it had been dried at the fire till it would lole no more of its weight, the pear gage exhibited a rarefaction of only 280. The leather was next held over the steam of hot water till it had recovered its former weight and moisture; and again the degree of exhaustion by the pear gage appeared to be 100,000. In all these three trials, the degree of exhaustion by the barometer
, gage never exceeded 268. Among the various substances afterwards included in the receiver, the four following likewise produced a degree of rarefaction estimated at 100,000, as indicated by the pear gage; viz. a piece of the inside of a China orange; some of the inside of an onion; a piece of tainted beef, and a piece of freih beef : each of these weighed 100 grains, and lost about two grains during the experiment. In none of these trials did the barometer gage indicate a greater degree of rarefaction than 160.
When oil of vitriol was put under the receiver, a very fingu. i Jar effect, and indeed contrary to those above mentioned, was produced : the pear gage then constantly indicating a much smaller degree of rarefaction than the barometer gage. this effect might possibly be owing to the vitriolic acid's attracting and condensing the aqueous vapour suspended in the air contained in the receiver. The acid acquired a small additional weight during each trial; part of which, however, it might collect from the open air, during the time spent in weighing it.
From another set of the Author's experiments, it appears, that when the receiver is placed, as is very usual, on leather foaked in water, or in spirit of wine and water, the pump is prevented from exhausting to any confiderable degree ; that is, according to the testimony of the barometer gage.--In a prelimi. nary trial, when the receiver was placed on the dry pump-plate, with only a little oil poured round the outside edge of it, the barometer gage and pear gage agreed in indicating a rarefaction of 600 as before: but when the receiver was set on wet leather, the rarefaction, in fix different trials, never exceeded 51. In these experiments it is observable that the degree of exhaustion, as indicated by the pear gage, varied, somewhat unaccountably, from soo to 16,000.
The bad effects resulting from the using of water in the barrel, or from employing it in softening the leathers of the pistons, are rendered evident by two of the Author's experiments ; where the highest degree of rarefaction that could be procured, under these circumstances, was 37 according to the barometer gage, and 38 according to the pear gage.
The effects of a vapour on the barometer gage, is in none of these experiments more conspicuous than in the 61st and Jatt. In consequence of putting a vial of æther under the receiver, for the purpose of producing artificial cold; though the pump was worked half an hour, the apparent degree of exhaustion, according to the barometer gage, was only 16:—and yet this very pump exhausted above 400 times, according to the same gage,
before the æther was put under the receiver. We shall just mention, by the bye, that, in the experiment preceding this, the Author produced a cold by means of æther, in the exhausted receiver, which was 48 degrees below o in Fahrenheit's thermometer ; that is 103 degrees below 55°. the temperature of the air in the room where the experiment was made.
These are some of the more material parts of Mr. Nairne's very ingeniou experimental investigation of this curious subject. We would recommend, however, the perusal of the whole
article, as well as the further prosecution of the inquiry itself, to
in the Hartz. By John Andrew De Luc, F. R.S.
• That even mercury, the heavielt of all known fluids, is elevated into vapour in the Torricellian vacuum, has been long observed by the Reviewer of the present article. In one barometer particularly, which terminares above in a large ball, he has during more than seven years past seen that part of the surface of the ball which was next to a window near which the instrument was suspended, studded with numerous mercurial globules, elevated from the furface of the quicksilver in the tube, which was at least five inches below it. Some of these, when they have acquired a pretty large size, roll down, and are succeeded by others. After repeatedly washing them down, by inclining the tube, fresh globules, though at first visible only with a magnifier, may be perceived in the space of a day or two, which afterwards increase both in number and fize. These globules never appear except on that side of the bulb next the window. On turning the tube half round, they gradually become smaller, and at length disappear; while a fresh succession of globules begin to appear on the opposite fide, or that which is now next the window.-Colonel Roy, in one of the following articles, takes notice of his having observed mercury converted into vapour, in vacuo, and condensed in the upper part of the tobe, in some of his experiments, when it was heated to 100°. F. and upwards. Our observation thews that this evaporation takes place in the common temperature of the atmosphere; and in the winter as well as fum. mer. Indeed, there are few barometers in which some mercurial globules may not be perceived, in a void part of the tube, on a near inspection. That an claffic vapour rises from heated water, in vacuo, and presses on the surface of the mercury, in the bason of the common barometer-gage, was observed by the Abbé Nollet. See Mem, de l Arad. des Sciences, Année 1748, pag. 122.
Edit, in 12mo. + See our Review, vol. xlviii. Append. p. 576. Vol. xlix, Append. p. 579, and vol. L. p. 567.
densations of the air, in deep pits, which contain exhalations of various kinds, follow the same laws with the rarefactions observed by him on the mountains in the neighbourhoad of Geneva; where the observations were made on which bis formula were founded. He gives in this article a detail of his subterra. neous barometrical observations, which were found to agree very nearly with the geometrical measures that had before been taken by the miners.
As some doubts might be entertained with respect to the accuracy of these last measures, which had been taken by the subterranean geometer, with scarce any other apparatus than a twisted brass wire five fathoms long, a semi-circle, and a com. pass; the Author remarks that these observations are of too much importance to the miners to be taken in a negligent or inaccurate manner. Daily experience, M. De Luc obferves, evinces the truth and exactness of these subterranean operations. Fully confiding in the truth of his observations, a miner-' in the absolute obscurity of the entrails of the earth, undertakes a labour that is to cost him years, in daily boring through a rock. Another miner sets out to meet him, from fome other mine, or from without. At the end of a determined measure, the gnomes begin to hear each other, and at length they meet. I have observed some of these points of rencounter in the galleries ; it is sometimes difficult to perceive the small winding which has been necessary for their meeting end to end.' Article 29. Observations made in Savoy, in order to ascertain the
Height of Mountains by Means of the Barometer ; being an Examination of M. De Luc's Rules, delivered in his Recherches, &c. By Sir George Shuckburg, Bart. F.R.S.
This philosophical traveller, in the course of a tour into Italy, in the years 1775 and 1776, made some stay at Geneva, and being provided with a large and excellent colle&ion of philofophical inftruments, he had the laudable curiosity, and the perseverance, to verify or repeat M. De Luc's barometrical experiments on the spot where they were originally made.-From feveral of his observations it follows, that some correction of the barometrical rules given by M. De Luc is necessary : we mean particularly with respect to the true ratio between the specific gravities of air and quicksilver; or in the expressing the value of an inch of quicksilver in the Torricellian tube, in corresponding inches of the acmosphere, the temperature being given.
From the mean of the Author's obfervations, on the Mele, and on Mont Saleve, one of M. De Luc's ftations, it may be inferred chat M. De Luc's rules give the difference of elevation too little by about 231 feet in every 1000 feet; and consequently that the atmosphere is rather lighter than he presumed it to be. The Author seems inclined to afcribe this error of lo
diligent and accurate an observer to his not having placed his barometers sufficiently near each other in an horizontal direction; whereas his were never feparated more than two or three miles.
The second part of this article consists of precepts, as well as tables, for calculating any accessible heights or depths. These are so constructed as to be easily understood by persons who are not conversant with logarithms, or mathematical computations. A table likewise is added of a great number of heights taken by the barometer, at various places in France, Savoy, and Italy..
The conclusion of the Author's description of his ascending the Mole--a steep insulated mountain eighteen miles east of Geneva-is sufficient to make the reader giddy.-'We had now,' says he reached the summit; and there my curiosity finished in astonishment. I perceived myself elevated 6000 feet in the atmosphere, and standing as it were on a knife edge, for such is the figure of the ridge or top of this mountain ; length: without breadth, or the least appearance of a plain, as I had expected to find. Before me an iminediate precipice, à pic, of above 1000 feet, and behind me the very steep ascent I had just now mounted. I was imprudently the first of the company : the surprize was perfect horror, and two steps further had fint me beadlong from the rock. Article 34. Experiments and Observations made in Britain, in
order to obtain a Rule for measuring Heights with the Barometer. By. Colonel William Roy, F.R.S.
These observations and experiments are intended still further to improve M. De Luc's barometrical method of mensuration; but they are too numerous and complicated to admit of any very satisfactory extract or abridgment. We shall briefly mention, however, a few of the results.
In the first section, the Author inquires into the rate of expansion of quicksilver by various degrees of heat, as ascertained by means of an apparatus contrived for that purpose; in which the mercury contained in a barometer tube had various temperatures communicated to it, from the freezing point to that of boiling water. From these trials it appears, that the mercury ftanding at 30 inches, in the temperature of 32 F. suffers, not an equal or uniform, but a progressive expansion, on being gradually affected by increasing degrees of heat: the expansions in the lower parts of the scale being greater than those produced in the higher temperatures. It appears too, that when the above mentioned mercurial column has acquired the heat of boiling water, it is lengthened bed parts of an inch. - In the second section, the Author endeavours to ascertain the expansion of air by heat, through the means of fthe manometer. From this set of experiments he infers that it is past a Rev. June, 1778.