height, that the pistons might move air-tight in them. From the cylinders, tubes passed to a common canal, terminating in the airpump plate, on which receivers to be exhausted were laid, as in Boyle's second engine. It is not a little singular that Papin's machine should have been overlooked by most later writers. It is not referred to in any recent English work of authority, although its curious stirrup arrangement, which has been employed in no English air-pump, might have been expected to direct attention towards it. Papin is mentioned incidentally by Nairne as an improver of the air-pump.-(Phil. Trans., 1777, p. 635.) Dr Hutton, in his Mathematical Dictionary (vol. i., p. 55, 1796), mentions Papin's two barrels and twin pistons, but not the stirrup arrangement. In Shaw's abridged Boyle, the whole machine is described and figured, but Papin's name is not mentioned. Recent writers on Pneumatics having overlooked Papin's machine, whilst they universally acknowledge the importance of two barrels with the pistons counterbalancing each other, have attributed this great improvement to Boyle, to Hooke, or to Hauksbee. Boyle's imputed claim to the honour of having first constructed a double-barrelled air-pump, may be summarily dismissed, as he himself disavows the honour, refers to Papin's air-pump as new to him, and ascribes its invention to Papin.-(Birch's Boyle, vol. iv., p. 506.) Mr Weld, however, puts Boyle's claim on another, and at first sight apparently satisfactory, basis. The Royal Society, according to the former, who is its assistant-secretary, possesses Boyle's original airpump, which has two barrels, and otherwise much resembles an airpump of the present day.-(History of Royal Society, vol. i., p. 96.) If, however, the instrument shewn to visitors to the Royal Society's apartments, be the earliest English air-pump, then Boyle was not only the first to employ a double-barrelled pneumatic pump, but his earliest pneumatical engine had two barrels. The instrument, however, which, as Boyle informs us ("Continuation of New Experiments, &c., on the Spring and Weight of the Air," Oxford, 1669, Preface), he gave to the Royal Society, in 1662, was his "Great Pneumatical Engine," which he described and figured in 1659. It had a single barrel, and was quite unique in its construction and appearance. The first double-barrelled air-pump to which Boyle refers is Papin's, with which he did not become acquainted till some seventeen years after he presented his earliest air-pump to the Royal Society. Mr Weld, therefore, is certainly mistaken in conceiving that the old double-barrelled pump in the Society's possession is Boyle's original air-pump. It is probably not an instrument of Boyle's century. Dr Thomas Young also supposes the first English air-pump to have had two barrels, and ascribes their introduction to Hooke.(Natural Philosophy, Kelland's edition, p. 278.) The latter, however, states distinctly, that the instrument he made for Boyle had one barrel (Waller's Life of Hooke, p. iii.), and his drawing of it, which is engraved in the vignette frontispiece on the title-page of the several volumes of Birch's Boyle, represents the great pneumatical engine as possessing but one cylinder. Professor Robison, in his treatise on Pneumatics, ascribes the double pump in one place to Hooke (Enc. Brit., 7th Ed., p. 80), and in another to Hauksbee (p. 93). Professor Robison does not refer to any writing of Hooke's as containing a claim, on his part, to the invention in question; and it is impossible to suppose that Hooke could have constructed a double air-pump before Papin did, without Boyle being aware of the circumstance. At all events, till it is shewn that Hooke himself claimed the double air-pump as his invention, it is unnecessary to discuss his supposed merits as its inventor. Hauksbee appears to have been the first Englishman who constructed an air-pump with two barrels. He described it in his Treatise entitled "Physico-Mechanical Experiments on various subjects, by Francis Hauksbee, F.R.S., 1709." It was constructed in, or about, 1704, so that it cannot come into competition with a double air-pump of Hooke's invention (if he ever devised one), seeing that he died in 1702. Still less can it supplant Papin's instrument, which was brought to England in 1676, and must have been known to Hauksbee. Hauksbee's air-pump was a combination of the rack and pinion of Hooke's pneumatical engine which he constructed for Boyle, and the two barrels, twin pistons, and self-acting valves of Papin's pump. From all, it appears, that no English claimant, at least, can dispute priority, so far as the double pump is concerned, with Papin. Winkler, who was Professor of Natural Philosophy at Leipsic in the middle of last century, in his Sketch of the History of the AirPump, refers to Hauksbee's as the first constructed with two barrels. (Elements of Natural Philosophy, 1757, English Translation, p. 119.) M. Libes (Histoire Philosophique des Progrès de la Physique, Paris, 1810–1812), mentions Papin and Hauksbee as the only claimants of the double pump (t. iii., p. 56); and adds, that Cotes, the mathematician of Cambridge, who was contemporary with Hauksbee, regarded Papin as the author of the invention. If there are no claimants known even to Continental historians of science, but Hauksbee and Papin, the latter, whose instrument was constructed more than twenty years before Hauksbee's, is entitled to the whole honour due to the inventor of the double air-pump. 2. On the Classification of Colours. Part II. By Professor J. D. Forbes. (See p. 190.) The object of this paper is chiefly one of nomenclature. Every one has felt the difficulty of describing with the precision the innumerable hues which occur in nature and in art; and which it is equally desirable for the optical philosopher, the artist, and the manufacturer, to be able to refer to in a clear and definite manner. But such a nomenclature or classification must proceed upon some admission as to the manner of compounding complex hues out of simple ones; and, therefore, the author first treats of the (so-called) Primary Colours. He admits it as highly probable, that all known colours may be formed out of Red, Yellow, and Blue; although, when we attempt to compound pigments, we have a very notable loss of light, and also an unavoidable impurity, which is most visible in the compound tints. The author, in passing, endeavours to explain clearly why the union of pigments never can produce a perfect white, although the coloured light of the spectrum does so; for, by adding blue light to yellow light, we not only change the colour, but we increase the illumination; whereas, by adding a blue to a yellow pigment, whilst we change the colour, we at the same time reduce the luminousness of the surface, the blue particles being far less reflective than the yellow ones. Inferring from Newton's empirical rule, the quantities of red, yellow, and blue light, which should combine to make white light; and adopting Lambert's results as to the reflective powers of the brightest pigments, the author concludes, that the mean illumination of a disk put in rapid revolution, and containing coloured sectors, will be 4.57 times less than if it reflected the whole incident light, or it will reflect only about half the light which white paper does under the same illumination, therefore it will appear relatively grey under any given The author then states, that the triangular arrangement of colours first proposed by Mayer, and farther carried out by Lambert, appears to afford the clearest and truest mode of displaying at a glance the modification of colour due to the varying proportion of the three primary elements. In this triangle, perfect red, yellow, and blue, оссиру the three corners; and these colours graduate into one another, according to the simple law of the distance of any point in the triangle from the three corners. The sides of the triangle are occupied by binary colours or compounds, by two and two; the interior is occupied by triple compounds; and the centre of gravity of the triangle ought to be a neutral grey. Hence it will appear, that any hue not purposely diluted with black or white, as composed of a compound of a binary colour with neutral grey. Hence a convenient nomenclature suggests itself as follows the first column containing the binary colours. * * * YELLOW. &c. &c. * * * &c. Greyish Orange. Grey Orange. Orange Grey. Orangish Grey. Grey. Greyish Yellow. Grey Yellow. Yellow Grey. Yellowish Grey. Grey, * These colours are supposed to be of the standard or maximum attainable intensity. They may be diluted with white on the one hand, forming tints; or with black, forming shades. Mayer's triangle may be repeated with these modifications; but as the colour tends to extinction, either in the direction of perfect blackness or perfect whiteness, the number of compartments in the triangles may be diminished as the dilution of the colours increases. Thus, the whole may be formed into a double pyramid of colour, converging to white above and to black below. The author has been much indebted to Mr D. R. Hay, the ingenious author of the "Nomenlature of Colours," and other works, not only for specimens of coloured papers formed by the actual mixture of the three primary colours, but also for many valuable suggestions, of which, in the course of this paper, he has freely availed himself. It is the author's wish to be able to obtain a series of coloured enamels complete, according to Mayer's and Lambert's classification. Some he has already obtained from the Vatican Collection (of which he gives a short description), and he hopes to render it more complete. 3. Verbal Notice of Siliceous Stalactites on Arthur's Seat. By Dr Fleming. Dr Fleming began by stating, that a paper of his, "On the Neptunian formation of Siliceous Stalactites," was read before the Society, March 7, 1825, and published in "Brewster's Journal of Science," for April of the same year, p. 307. To this paper Dr Hibbert has referred, in his description of the "Limestone of Burdiehouse," Edin. Phil. Trans., vol. xiii., p. 280, but has misrepresented, in an unaccountable manner, the facts which had been stated. Dr Fleming, expressly said, in describing a limestone containing the remains of dicotyledonous plants, and consisting of flinty and calcareous layers, that it" dips under the great bed of limestone belonging to the coal formation which extends north towards Linlithgow," which "encloses the remains of those marine animals which are common in the limestones of the coal formation." Dr Hibbert, on the other hand, confounds the two beds, or rather represents the bed with the vegetable remains as having been viewed as identical with the bed of limestone with marine remains; for he adds, "Dr Fleming's remark, that this limestone encloses the remains of those marine animals, which are common in the limestones of the coal formation, I consider as a mistake." The limestone, however, with vegetable remains, had been described as differing in structure, and occupying a lower position, than the limestone with marine remains. Dr Fleming then stated that, in the paper referred to, he had described siliceous stalactites as occurring in the trap-rocks of the north side of Fife (a prolongation of the Ochils), and for some time looked for similar concretions, in vain, in the corresponding rocks of Arthur's Seat. Lately, however, he had detected them, hanging from the under surface of a bed of porphyry interstratified with laminated clay, at the Bog-Crag on the east side of the Hunter's Bog. The aqueous origin of the stalactites would not now be disputed, nor, in the present state of chemistry, would their occurrence excite surprise. |