affords twelve times as much light as a good wax-candle of an inch in diameter. 94 The variation that occurred in the quantity of light emitted by a common wax-candle in an hour, the candle being fnuffed when neceffary, was found to be between 100 and 60. The light of an ordinary tallow-candle, juft fnuffed and burning with its usual brightness, was as 100; in 11′ it was as 39; in 8' more it was 23; and in 10' more, or 29' after it had been snuffed, its light was reduced to 16. When it was again fnuffed, it recovered its ufual brilliancy. By farther experiments, which our limits, already exceedea, will not allow us to recite, it appears that the consumption of bees-wax is to that of olive-oil, in the production of the fame. given quantity of light, as 100 to 129; the consumption of olive-oil to that of rape-oil as 129 to 125, and to that of linseedoil as 129 to 120. When a tallow-candle burned with a clear bright flame, the confumption of the olive-oil to that of the tallow was as 129 to 101: but, when the candle burned with a dim light, the former was to the latter as 129 to 229. Hence it appears that the tallow, inftead of being nearly as productive of light in its combuftion as bees-wax, as it appeared to be when the candle was conftantly well fnuffed, was now, when the candle was fuffered to burn with a dim light, by far lefs fo than oil. It is ftill more extraordinary that the very fame candle, burning with a long wick and a dim light, actually confumed more fallow than when properly fnuffed, and when it gave nearly three times as much light. The author has collected these facts in a table, fhewing the relative expence of bees-wax, tallow, olive-oil, rape-oil, and linfeed-oil, in the production of light; and he clofes this article with a brief account of feveral experiments for afcertaining the tranfparency of flame. This fact may be easily determined by a very simple experiment. The flame of a lighted candle at noon-day, when the fun fhines with moderate brightness, holden between the eye and the fun, entirely dif appears. This will be the cafe even in a fituation where the light is not ftrong enough to dazzle the eye fo much as to prevent its feeing, very diftinctly, the body of the candle and the wick, To this paper are added four tables, exhibiting the various parts of the photometer in its laft and moft improved state. An Account of fome Experiments on coloured Shadows. By the fame. In the profecution of his experiment on light, the author was furprised by an appearance that was not only unexpected, but in the highest degree ftriking and beautiful. He found that it is abfolutely impoffible to produce two fhadows at the fame time from the fame body, the one answering to a beam of L 3 day day-light, and the other to the light of a candle or lamp, without thefe fhadows being coloured, the one yellow, and the other blue.' In order to afcertain this fact, nothing more is neceffary than to J Take a burning candle into a darkened room in the day-time, and open one of the window fhutters a little, about half or three-quarters of an inch for inftance; when the candle being placed upon a table or ftand, or given to an affiftant to hold, in fuch a fituation that the rays from the candle may meet those of day-light from without, at an angle of about 40%, at the furface of a fheet of white paper, held in a proper pofition to receive them, any folid opaque body, or a cylinder, or even a finger, held before the paper, at the distance of 2 or 3 inches, will project two fhadows upon the paper, the one blue, and the other yellow.' By altering the diftance of the candle from the paper, or by opening the window-fhutters more or lefs, thefe coloured fhadows may be made to pass through all the gradations of fhade, from the deepest to the lighteft, and vice verfa.' That the colours of thefe shadows are owing to the different qualities of the light by which they are illuminated, is certain: but as to the manner of their production, the author is not fatisfied. Apprehending that the difference in the whitenefs of the two kinds of light might, in fome way or other, occafion the different colours of the fhadows, he attempted to produce the fame effects by employing two artificial lights of different colours; and he fucceeded completely. In a dark room, the light of two burning wax-candles was made to fall on the white paper at a proper angle, in order to form two diftinct fhadows of the cylinder: but these fhadows were found not to be in the leaft coloured. By afterward interpofing a pane of yellow glafs, approaching to a faint orange colour, before one of the candles, one of the fhadows becane yellow, and the other blue. When equal panes of the fame yellow glafs were interpofed before both the lights, the white paper affumed an orange hue, while the fhadows were untinged with any colour:-but, when two panes of the fame glafs were interpofed before one of the lights, and only one pane remained before the other, the colours of the shadows immediately returned. Having thus confirmed his fufpicions that the colours of the fhadows arofe from the different degrees of whiteness of the two lights, the author endeavoured, by bringing day-light to be of the fame yellow tinge with candle-light, by the interpofition of fheets of coloured glafs, to prevent the fhadows being coloured when day-light and candle-light were together the fubjects of the experiment. In this alfo he fucceeded, and was able to reverfe the colours of the fhadows by causing the daylight to be of a deeper yellow than the candle-light. In the course of thefe experiments, (fays he,) I obferved that different fhades of yellow given to the day-light produced very different and often quite unexpected effects: thus one fheet of the yellow glafs interpofed before the beam of day-light changed the yellow fhadow to a lively violet colour, and the blue fhadow to a light green; two fheets of the fame glafs nearly defroyed the colour of both the shadows; and three fheets changed the fhadow which was originally yellow to blue, and that which was blue to a purplish yellow colour. When the beam of day-light was made to pafs through a sheet of blue glass, the colours of the fhadows, the yellow as well as the blue, were improved and rendered in the highest degree clear and brilliant; but when the blue glafs was placed before the candle, the colours of the fhadows were very much impaired.' Having contrived an apparatus, adapted to the profecution of his inquiries respecting coloured fhadows, he made a variety of experiments with a view of inveftigating the caufes of appearances, which ftill feemed to be enveloped in much obfcurity and uncertainty:-but these experiments we cannot recite. From the great variety of colours which he observed in the course of these experiments, many of which did not seem to have the least relation to the apparent colours of the light by which they were produced, the author began to fufpect that the colours of the fhadows might, in many cafes, notwithstanding their apparent brilliancy, be merely an optical deception, owing to contrast, or to fome effect of the other neighbouring colours upon the eye.' The Count fuggefts that the experiments, which he performed for determining this fact, may enable us to account for the apparent blue colour of the fky, and the great variety of colours which frequently adorn the clouds.' He adds, I believe it is a new difcovery, at leaft it is undoubtedly a very extraordinary fact, that the eyes are not always to be believed, even with respect to the prefence or abfence of colours.' One circumstance here deferves to be mentioned; and that is The most perfect harmony which always appeared to fubfift between the colours, whatever they were, of the two fhadows; and this harmony feemed to me, (fays the author,) to be full as perfect and pleafing when the fhadows were of different tints of brown, as when one of them was blue and the other yellow.' The appearances of thefe colours, he adds, were quite enchanting; and he concludes with fuggefting that the profecution of these experiments may not only lead to a knowledge of the real nature of the harmony of colours, or the peculiar circumftances upon which that harmony depends; but that it may also enable us to construct inftruments for producing that harmony, for the entertainment of the eyes, in a manner fimilar to that in which the ears are entertained by mufical founds.' Some of the facts recited in this paper will bring to the recollection of our philofophical readers the obfervations that have been made by others on the blue fhadows of bodies. They L 4 were were first observed by Otto Guericke, and noticed again at the distance of about a century, viz. in 1742, by M. Buffon. The Abbé Mazeas has recorded the phænomenon, and attempted to explain it. Melville and Bouguer, about the fame time, directed their particular attention to this curious appearance; and they afcribe it either to the atmosphere or to the vapours that are blended with it, which intercept the paffage of the faintercoloured rays, and reflect them on other bodies. Thus they account for the blue colour of the sky, and for the blue shadows projected by opaque bodies that are illuminated by the fky-light. The numerous obfervations of M. Beguelin, on this fubject, deferve peculiar notice. We have an abftract of them in Priestley's Hiftory, &c. of Light and Colours, p. 441, &c. The new facts recited by the present ingenious auther, and the circumstances attending them, are curious and interefting: but, in the perufal of his paper, we were led to imagine that the experiments and obfervations, made by former writers on the subject of his inquiry, and which have occafionally fome refemblance to his own, had escaped either his notice or his recorlection. He expreffes furprise at appearances which, adverting to fuch experiments, he might naturally have expected; and, when he is relating facts fimilar to thofe recorded by fome of the writers whom we have named, he makes no mention of them. Some Facts relative to the late Mr. John Hunter's Preparation for the Croonian Lecture. By Everard Home, Efq. F.R.S. The fubject which Mr. Hunter had felected for the CROONIAN lecture was the ftructure of the cryftalline humour of the eye; but, as he died before he had an opportunity of completing his obfervations, Mr. Home has here ftated the facts which Mr. Hunter propofed to have difcuffed, and the experiments by which he intended to have established them. It was his opinion that the crystalline humour was enabled by its own internal actions to adjust itself, fo as to adapt the eye to different diftances, In diffecting the eye of the cuttle-fish, He found it compofed of lamina, whofe appearance was evidently fibrous, for fome depth from the external furface; but becoming less and lefs diftinct, till at last this fibrous appearance was entirely loft, and the middle, or central part of the humour, was compact and tranf pareat, without any vif.ble lamina. From this ftructure it would ap pear, that in the eye of the cuttle-fifh the exterior parts of the hu mour are fibrous, the interior parts not; fo that the central part is a nucleus round which the fibrous coverings are placed.' As there is no difference between the ftructure of the cryf talline humour in the cuttle-fifh and that of other animals, except in the diftinctness of the fibrous appearance, Mr. Hunter 8 concluded concluded that the exterior part in all of them was fimilar, although no appearance of fibres could be demonftrated. His experiments were, therefore, Founded upon the analogy that ought to exift between this humour, if mufcular, and others of a fimilar ftructure, which led him to expect that they would be acted upon by the fame ftimuli; and having found that a certain degree of heat, applied through the medium of water, will excite muscular action, after almost every other ftimulus had failed, it was propofed to apply this to the crystalline humour, and ascertain its effects. The cryftalline humour taken from animals recently killed, must be confidered as being ftill alive. Such humours were to be immerfed in water of different temperatures, and placed in fuch a manner as to form the image of a lucid well-defined object, by a proper apparatus for that purpose, so that any change of the place of that image from the ftimulating effects of the warm water upon the humour would be readily afcertained. Thefe were the experiments which Mr. Hunter had inftituted and begun; but in which he had not made fufficient progress to enable him to draw any conclufions.' As Leuwenhoek had obferved and defcribed the fibrous ftructure of the cryftalline humour, our author afcertains the peculiar fact for the discovery of which we are indebted to Mr. Hunter. To him we owe the discovery of an eye in which this ftructure of the cryftalline humour was perfectly distinct, and in which all the circumstances, of courfe, and fituation, could be determined.' We regret, in common with other friends of science, the melancholy event which has prevented the experiments and obfervations, by which it was proposed to demonftrate that this ftructure is capable of producing confequent actions and effects fufficient to explain the adjustment of the eye to different diftances. The author of this paper is well qualified for profecuting the experiments which, by Mr. Hunter's death, are left incomplete, and for applying them to the elucidation and proof of the fact which he wished to establish. This part of the volume concludes with the meteorological journal for the year 1793: the fecond part is published, and we Thall speedily attend to it. ART. V. A Courfe of Lectures on the principal Subjects in Pneumatology, Lectures a diftinguished place in the fcale of merit. His judicious and indefatigable labours as a Chriftian minister, as a tutor |