of water, to which he adds their tenacity and friction. We muft refer the curious Reader to the Memoir itself, as the details it contains are not susceptible of such an abridgment as would render them intelligible,-and the plates also are necessary for this purpose.

SPECULATIVE PHILOSOPHY.

Mem. I. Confiderations on the First Tufculan of Cicero, concerning Death. By M. FORMEY. There is much more good fenfe and true philofophy in thefe Confiderations, than we have ever found in the Dialogues of Cicero which occafioned them. The high veneration we have for that illuftrious Roman does not dazzle us so far as to prevent our perceiving the want of method, the contradictions, the puerilities, and fophifms, that form an unpleafing contraft with many fine paffages in this First Tufculan. Certain it is, that M. FORMEY ftates the case with much more precision than Cicero has done. If death, fays he, is the final term of our exiftence, we are no longer either happy or unhappy when it arrives. But if there be another life after this, we may, in this cafe, either hope for happiness, or fear the contrary, in a future ftate. In the former cafe, those who defire to live, or to have their exiftence prolonged, cannot, if they reflect at all, think of death, and its inevitable approach, which renders their exiftence but a tranfitory meteor in the night of eternity, without anxiety and pain. The brute naturally dies, as it has lived, without reflection on the present, or anticipation of the future, and confequently with indifference; but man, who has carried to a certain degree of improvement the powers of reafon and the capacity of enjoyment, and is ever cafting his thoughts forward beyond the prefent moment, muft voluntarily place himself in the fphere of the brute, when he beholds death with indifference,-which, if it be real, and not pretended, is rather to be deemed ftupidity than fortitude.On the conjectural fuppofition of another life after this, a reafonable being ought to adhere to fuch principles, and fuch a line of conduct, as will most probably tend to better his condition in a future scene. But on every fuppofition, death is an awful thing; and it is not a mark of pufillanimity to think of it with a certain inquietude, as it terminates all our enjoyments, and diffolves all our most interefting connections. The title of the Firft Tufculan is, Concerning the Contempt of Death; and this fentiment is inculcated into the difciple of Cicero with great fuccefs; yet in this fame Dialogue Cicero tells us, that the lift of the WISE man is a continual meditation upon death. Now, it is a very strange kind of wifdem which is perpetually occupied upon an object that is contemptible. According to M. FORMEY, the wife man will think frequently of death, render the idea of it familiar, meet it with a modest dignity, without those indecent pleasantries

pleafantries on the one hand (which have been thrown out by certain pretended great men in their dying moments, and related by their panegyrifts as redounding to their honour), and alfo without those vain lamentations on the other, which only increase the bitterness and anguish of their departure.'-There is, furely, fterling fenfe, and found philofophy, in this view of the fubject.

There are many more judicious obfervations on the subject in this Memoir, which, however, is employed in feverely criticizing, and often in expofing to ridicule, the reasonings of Cicero on the immortality of the foul, which are contained in the First Tufculan. M. FORMEY is prolix and talkative in this analyfis, but he is more lively, fmart, and entertaining, than critics generally are, especially when advanced in years, as he is. Cicero fays, that he never varied in his belief of the foul's immortality; but our Academician thinks he did. Socrates and Cicero were', fays he, in the fame ftate of mind with respect to this object; they ardently wifhed for immortality, and in certain moments, entertained a perfuafion of it which they took for conviction; but, at other times, a cloud arofe which obfcured the profpect. This,' continues he (with more levity and pleafantry, than equity and candour), puts me in mind of a learned courtier, well known to this aflembly, and beloved by us all, who faid, that in fummer he believed the immortality of the foul, but doubted it in winter. - Where is the man whofe conviction is at all times equally clear and unclouded?

Mem. II. Reflections on Games of Hazard. By M. D'ANIERES. Mem. III. On the Distinctions between COMMON SENSE, JUDGMENT, TASTE, SENTIMENT, WIT, IMAGINATION, GENIUS, and TALENT,-together with fhort Reflections on Eloquence, Style, and Tranflations. By M. SECONDAT. This ingenious writer is the fon of the celebrated Prefident De Montefquieu, and has inherited a portion of his nice penetration and elegant tafte. There is nothing, however, in this Memoir fufficien ly new or interefting to require particular notice. The reflections it contains are fhort, fententious, fometimes just, frequently plaufible, and now and then obfcure.

BELLES LETTRES.

Mem. I. Concerning the true Wealth of Nations, the Balance of Commerce, and the Balance of Power. By the Count DE HERTZBERG, Minifter of State, and Rector of the Academy. This excellent Differtation has been already reviewed in the English tranflation of it, published by Dr. Towers. See p. 42. of the Review for January 1787.

Mem. II. On the Influence of the Sciences on Poetry. Fifth Memoir. By M. MERIAN. This ample Differtation, which con

tains

tain 100 pages, is entirely employed in the inveftigation of the origin of Italian poetry, and more especially in treating of the language, learning, and genius, of Dante; alfo of his imitations, and his imitators.

ART. X.

Defcription of an improved Air-pump; and an Account of fome Experiments made with it: By JoHN CUTHBERTSON, Mathematical Inftrument Maker in Amsterdam. 8vo. Amfterdam. 1787.

HOUGH the air-pump was invented above a century ago,

THO

it has not been brought to that degree of perfection which might have been expected from its long and generally acknowledged utility in phyfical inquiries. It was indeed greatly im proved by the ingenious Mr. Smeaton; but even his conftruction left feveral imperfections unremedied. One of these was occafioned by the preffure of the pifton upon the valve that opens to let the air into the barrel from the receiver. This defect Mr. Cuthbertson removed fome years ago, by placing this valve on one fide of the barrel; and of this improvement he gave a description, in the Dutch tranflation of Dr. PRIESTLEY'S Obfervations and Experiments on different Kinds of Air, published in 1781.

With pumps of this conftruction, dry air might be rarified about fix hundred times: this feemed to be the highest degree of perfection of which the pneumatic engine was capable; for the reason of its not exhaufting further was evidently the weakened elafticity of the air remaining in the receiver, which decreafing in proportion as the quantity is diminished, becomes at length infufficient to raise the valves that open a communication between the receiver and the barrels, fo that no more air can pass from the former to the latter.

This defect was, however, in fome measure removed by Mr. Haas, who, by means of a pin fliding through a collar of leathers, enabled the operator to push up the undermoft valve, when the elafticity of the air was too much diminished to raise it. But, for want of a fimilar contrivance to open the valve in the piston, which was equally neceffary, the improvement was incomplete. Befide, the additional mechanifm rendered the machine more liable to become leaky, and thus increased an inconvenience which is common to all air-pumps that are made with valves.

Thefe imperfections feem to be entirely removed by the ingenious contrivance of Mr. CUTHBERTSON, whofe air-pump has neither cocks nor valves, and is fo conftructed, that what fup

plies their place has the advantages of both without the inconveniences of either. A particular defcription of the mechanism of the inftrument would not be eafily comprehended without the plates.

Mr. CUTHBERTSON, not finding the long barometer gage, as it is commonly used, fufficiently exact, has improved it, by immerging, in the fame ciftern, a barometer tube, filled with mercury well purified from air: these tubes are bound together, fo as always to ftand parallel to each other, and furnished with a fliding fcale, by which the difference between the height of the mercury in the gage and barometer tubes may be difcerned with the greatest exactnefs, even to the hundredth part of an inch. Another gage here described is of his own invention, and is in the form of a double fyphon, in which the degree of exhaustion is estimated alfo by the difference between the height of the mercury in the two legs. Thefe gages were found always to indicate the fame degree of rarefaction.

It is well known, that if the receiver be placed upon leather, either oiled or foaked in water, this, when the preffure of the air is diminished, will yield an expanfible vapour, which will drive. out a great part of the remaining permanent air, and fill up its place in the receiver; but our Author has found that none, or at leaft very little of this vapour, is yielded by leather dreffed with allum, if it be foaked in hogs-lard: this therefore he recommends in common experiments; but when the utmost degree of exhauftion is required, his advice is, to dry the receiver well, and fet it upon the plate without any leather, only smearing its outfide edges with hogs-lard, or with a mixture of three parts of hogs-lard and one of oil. The ufe of the leather has long been laid afide by our Englifh mathematical inftrument makers, a circumftance which probably has not come to Mr. Cuthbertson's knowledge.

As in this machine there are no valves to be forced open, nor any thing to prevent the air in the receiver from expanding itfelf to its utmoft degree, it is eafy to conceive that its exhaufting power must be much greater than that of air-pumps as they are commonly conftructed. With this, however, as with all other inftruments of the kind, the degree of exhauftion that can be produced is different at different times, and depends much on the ftate of the atmosphere, being always greatest when this is moft free from moisture. From the experiments here related, it appears, that in fine weather the barometer and fyphon gage may generally be made to indicate a rarefaction of twelve hundred times; but, when the atmosphere was very dry, the exhaustion has been fo complete, that the gages have fhewn the air in the receiver to be rarefied above twenty-four hundred times. Thefe

These air-pumps are fo conftructed, that they may be made to condenfe, either at the fame time that they exhauft, or feparately; in the former cafe, the air, exhaufted out of one receiver, may be forced into another; and those with two barrels are so contrived, that either of these may be used independently of the other.

Befide the experiments which tend immediately to fhew the great degree of rarefaction which may be effected with this machine, Mr. CUTHBERTSON has related fome, in which the electric fluid was made to pass through a glass tube two feet and an half long, while under exhauftion. When the air in this was rarefied fourteen hundred times, it conducted so well, that the fparks from the prime conductor connected with it, which, before exhauftion, had been two inches, were only one fortieth part of an inch in length; and in the middle of the tube there was a space, fix inches long, entirely void of light, which at its two extremities appeared of a faint white colour. Our Author has also added fome experiments on the elaftic vapour which is emitted in vacuo by leather and other moist fubftances. One of thefe, in which this expanfible fluid is vifibly diftinguifhed from air, is fo ingenioufly contrived, that we shall conclude this article with an account of the manner of performing it.

For this purpose, the air must be made to pass from the barrel into the atmosphere through an inverted glafs fyphon, about half full of water; let a piece of leather dreffed in allum, about an inch fquare, be tied to a piece of lead; and, putting it into a glafs, pour upon it tranfparent lamp-oil, about half an inch higher than will cover it. This being fet upon the plate under a receiver, and gradually exhaufted, the leather will emit the air contained in it, which will be feen to rife in bubbles through the oil into the receiver, whence it paffes through the barrels of the pump into the fyphon, and will afcend in bubbles through the water, into the air. But, when the preffure of the air in the receiver is fo far diminished, that the gages become stationary, the expanfible fluid contained in the leather will affume the form of air, and likewife afcend, through the oil, into the receiver; but it will be found that, though the bubbles rife very quick, and in great abundance, through the oil, none will be feen, as before, to afcend in the water; because the elaftic vapour, as foon as it enters the fyphon, is condenfed by the preffure of the atmosphere, and reduced to its former ftate, in which it cannot produce any fenfiole effect.

ART.