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capable of such improvement, as would, at once, promote both public and private interest.

Thus have we endeavoured to give a general view of the work before us; wherein we meet with many useful, many trite, and some erroneous observations; the whole frequently obscured by a multiplicity of needless words, which we would advise the Author, by all means, to get retrenched, in care another edition of his book hould happen to be called for : in which view the corre&ting hand of a judicious friend (whi foould be an experienced farmer) might be of great use, as few people can bring themselves to a resolution of sufficiently retrenching their own superfluities.

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ART. IV. Rational Recreations, in which the Principles of Numbers

and Natural Philofopby are clearly and copiously elucidated, by a Series of ealy, entertaining, interesting Experiments ; among wbich are all rbofe commonly performed with the Cards. By W. Hooper, M. D.

8vo. 4 Vols. 1l. is. Boards. Davis. 1774. IT is the principal object of the experimental philosopher to

I inquire into the causes of natural appearances, by placing bodies in different situations, observing the results, and thence deducing their general properties, as well as their particular relations to each other. Of the numerous experiments that have been made with this design many exhibit such fingular and striking phenomena, as never fail to excite the attention even of the most incurious spectator ; who, while he receives amusement from the fingular or pleasing appearances exhibited to his view, may perhaps at the same time stumble upon instruction, and acquire some useful information concerning the principles which produce them. Several writers of the last and present century have accordingly endeavoured to dress up phiJorophy in this alluring garb; and have made collections of the more pleasing or singular experiments. From these the present Author has compiled the work before us, in which, likewise, a few original experiments are added to those of his predeces. fors; and he has presented others under a new face, so as to render them more striking or amusing: illustrating the whole by a confiderable number of plates.

The experiments, or recreations, as the Author terms them, which are contained in this work, are classed under certain general heads; to each of which is prefixed a set of aphorisms and propositions relating to each particular subject. In an ada vertisement (which is followed by an introduction much too florid and declamatory for the occasion) the Author assures us that the principles of each science are here laid down in a few plain aphorisms, such as require no previous knowledge, and very Little capacity or attention to comprehend. We think, on the

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contrary, contrary, that the reader, who has no previous knowledge; must be possessed of a very great capacity, and have a peculiar facility in the acquisition of science, joined to an uncommon thare of attention, to profit greatly by these aphorisms, or apply them to the explanation of the experiments to which they are prefixed.

In compiling this collection the Author seems to have Thewn rather too strong a propensity to gratify the passion for the marvellous; not only by the whimsical and singular titles which he gives to some of the most common philosophical experiments, (such as the magical bottle, the marvellous veffel, &c.) but by the large space which he has allotted to other marvellous performances very diftantly allied to philosophy. A confiderable, and much too great a portion of this work, is adapted to qualify the Author's pupil to become rather a. conjuror than a philosopher : a very large part of it being appropriated to the performance of experiments, vulgarly called tricks, with cards; some of which are so complicated, and depend so much on a peculiar address, as to appear to us rather the objects of a serious study than a recreation. A moderate number of recreations of this nature might have been properly enough admitted into a work of this kind ; merely to give an inquisitive reader a little insight into some of the methods employed by a Comus and a Jonas to lay our understandings asleep, while they impose on our senses by their hasty and hidden manoeuvres. But there is too much of this particular fpecies of · Recreative Philofophy' in this performance; and after all, we doubt whether the Author, or those from whom he copies, are quite in the secret of these sages. We have seen many tricks performed by Jonas, of which we do not discover the rationale in this work. .

Out of the numerous articles in the different parts of this performance, that come under the class of conjuration, we shall select only one piece of legerdemain as a specimen, which is, of a simple kind, and which we give for that reason. It is intitled The Transposable Pieces. Instead of transcribing the Author's chapter, we shall relate the trick in our own manner:

A conjurer exposes to the view of the company a guinea in his left hand, and a shilling in his right. He shuts both hands, and keeping them asunder tells them that by the power of his art the pieces shall change places. Without any visible manæuvre, except that of opening his hands, he immediately presents to the spectators the shilling in his left band, and the guinea in his right, and forthwith proceeds to some new trick, to prevent inquiry

To those who know the trick already we are almost alhamed to offer an explanation ; but for the sake of such as may be unacquainted with it, or may not already have guelled at it, we

thom conjurer expand a shilling der tells them without his left and keeping then change places hand

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Hooper's Rational Recreations.

21 thall add that the two pieces which we have taken the very al. lowable liberty, in our affumed character of conjurors, to call a guinea and a fhilling, are not Itrialy what they appear to be. Previous to the performance, two guineas and two shillings are ground down on one side to about half their usual thickness. Each of the guineas, thus diminished, is neatly riveted to one of the diminished shillings; so that each of the two pieces, when laid on the palm of the hand, appears to be either a guinea or a shilling, according as the one or the other moiety is uppermost. The trick is easily performed by turning them over, in the act of Tutting or opening the hand.

This is the only specimen that we shall give of the legerde. main so abundant in this performance. Laying aside therefore our cap and wand, we shall proceed to give an account of the distribution of the other matter contained in this work; adding occasionally a specimen or two of the Author's recreations.

The first volume contains a variety of problems, experiments, or recreations, depending on numbers, of which tricks with .. cards, as usual, constitute no inconsiderable part. To there, as connected with the doctrine of combinations, are added dif. ferent methods of writing in cypher, and decyphering.

In the second part of this volume the Author exhibits various experiments relating to Mechanics. The subject of the sist recreation is ' A clock to go perpetually, by the influence of the celestial bodies.'

A common clock is to be placed near a wall against which the tide flows. "To each of the barrels, round which the string that carries the weight is wound, there must hang a bucket, and into that, when the tide rises to a certain height, the water runs, by means of a pipe fixed in the wall. The bucket then over balancing the weight, descends, and winds up the clock; but when it comes to a certain depth, it is taken by a catch fixed in the wall, which, by turning it over, discharges the water. The weights of the clock then descend in the usual manner, and the buckets are drawn up.

« Now as this clock is kept in motion by the cide, and as the tide proceeds from the influence of the fun and moon, it necessarily follows, that the motion of the clock proceeds from the fame cause ; and that as long as the parts of the machine remain, motion will be perpetual-though not, as the Author afterwards observes, in the senfe usually affixed to the term by the mistaken advocates for a perpetual motion; but according to the vulgar acceptation of the phrase, in which fense every mill driven by a constant stream, or every smoke-jack moved by a constant fire, may be faid to be a perpetual motion.

In the second volume are contained some of the many amufing experiments with which the science of Optics furnilbes the

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experimental philosopher. Of these we shall particularise a curious deception, which we shall endeavour to explain without the use of figures. For the description of it the Author quotes M. Guyot, but it was originally published by Father Bonaventure, author of the Amusemens Philosophiques * We shall collect the principal circumstances of the experiment,' from the account given of it by the original author.'

If a vial half full of water be held upright before a concave mirror, and beyond its focus, the image of the vial will be seen inverted, before the mirror ; but the water contained in the body of the vial, instead of being inverted likewise, or appearing uppermost in the image, will there appear to occupy the lowest part, or the space between the mouth of the vial and its middle. If the bottle be held inverted, with its mouth stopped, its image will appear erect, but the water will seem to occupy the space between the bottom and middle of it. In both cases, that part of the vial which contains the water will appear empty, in the image, and vice versa.

If, while the vial continues inverted, the water be suffered to drop slowly from its mouth, the image of the vial will seem to fill in proportion as the vial itself is emptying: but at the instant when the latter becomes perfectly empty, the illusion suddenly ceases, and the image appears perfectly empty likewise. Further, if a few drops of water fall from the protuberance in the bottom of the inverted vial, they will, in the image, exhibit the appearance of so many bubbles of air, rising from the bottom of the vial to the surface of the water contained in it.

Father Bonaventure's conjecture concerning the cause of these fingular deceptions is ingenious, and appears to be well founded. We have always, he observes, been so accustomed to see water occupy the lowest place in a vessel; and at the same time the difference in appearance between the full and the empty part of the vial is so little, on account of the purity and perfect transparence of the water, that the mind habitually fees the fluid where it is not, and does not see it where it really is, notwithstanding all our reasonings and reflections to the contrary.

This deception, as we have observed, may generally be conquered, and the water be seen in its true place, or in contact with the bottom of the vessel, when its image is inverted, by trying the experiment with a wide - mouthed glass tumbler, especially on thaking the vessel. During the agitation of the water, its apparent lower surface in the image, supposing that

• See the Appendix to our 29th vol. page 490, and to vol. xliii. page 533•

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the illusion should still continue, will be seen to remain unmoved, and never to descend below the mouth of the glass, as it will seem to the spectator that it ought to do, were it really the image of the water.

As few persons are in possession of concave mirrors, we shall add that these experiments will equally succeed, if the vial be viewed through two convex lenses (two of the eye-glasses of a common telescope, for instance, or two spectacle glasses of a thort focus) placed at the distance of their common focus, so as to exbibit objects in an inverted situation.

Under this division of the work, and in the 42d recreation, the Author gives a short account of Colorific Music. Thole who are not conversant in foreign philosophical literature may perhaps be startled at the fingularity of the term. As chis species of meloiy is very little known in this country, we hall give a description of the grounds of it; not on account of the thing itself, but because we consider it as a singular phenomenon in the intellectual world, that a philosopher, and a man of ingenuity, Father Castel, who was the inventor of this proposed gratifica. tion of the eye, could possibly bestow so much thought, and spend so much time as he is known to have done, in the pur. fuit of lo unattainable a phantom.

Sir Isaac Newton first observed that the length of the spaces occupied by the seven primary colours in the solar speelrum happened to correspond, not to the lengths, as our Author says, but to the intervals in the monochord that express the seven notes in the diatonic scale of music. Laying hold of this ana. logy, which has little more than the single accidental coinci. dence abovementioned to support it, Father Castel proceeded so far as to con:rive, and, if we mistake not, to construct a singular machine, to which he gave the name of the Clavecin Oculaire, or the Ocular Harpsi hard: expecting that the eyes of the beholders would be gratified by the succession, or the admixture, of the different colours in his prismatic gamut ; as the ears of an audience are regaled by the melody, or the harmonious combination, of the supposed correspondent tones and semitones in the scale of Guido.

M. de Mairan has long ago shewn the various defects in this supposed analogy between sound and colours + : but were it much more perfect than it has been supposed, it is sufficiently evident, even a priori, or without any trial, that we are not formed to receive pleasure from coloured thirds and fifths, in any respect, or degree, resembling that which results from a mixture or succession of sounds. Certain colours are undoubtedly pleafing

+ See Memoires de l'Acad. Roy, de Sciences de Paris, année 1737, page 34, Dutch edition.

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