pratica di Pittori et la ragioni d'essa." (Or was this a diminishing mirror?) His secret for the composition of metallic mirrors is, three parts tin, and one copper. Upon this alloy, when in fusion, throw (for every pound) one ounce of tartar, and half an ounce of arsenic." The chapters on the art of pottery, and making lime, appear to contain nothing remarkable. The same may, perhaps, be said of the chapters relating to artillery and fireworks; but with these subjects, I have no acquaintance. The concluding chapter is perfectly characteristic of the Italian. "Del Fuocho che consuma et non fa cenere, et e potente pui che altro fuoco, del quale ne e Fabro el gran Figlio di Venere." "Chealtro dir non virole che cupido." Upon the whole, although this scarce volume from its meagreness and imperfections forms a singular contrast to the bulk and fullness of detail which might be expected in a metallurgical encyclopædia of the present day, it is unquestionably for its age a work of no common merit and interest; and the author is fairly entitled, from his practical intelligence and industry, to be ranked among those who contributed to realize the almost prophetic verse of his immortal countryman : 66 Esperienza Ch' Esser suol fonte a i rivi di nostri arti."-(Dante Paradiso.) I subjoin the account of the manufactory of Niello from the original: "Niellasi ancora per ornamento de lavori certi intagli o profili et questo prima si compone pigliando una parte di argento fino, due di rame, et tre di piombo fino, et in un vaso di terra che habbi el collo stretto et longo sempee la meta di solfo macinato, et sopravi si gitta fusi gli detti metalli, et con terra subito messi si' chuida la boccha del vaso, et benissimo si rimena. Dipdoi freddo rompendo il vaso se ne cava et netta, et lavasi et alfin si macina, et adoperasi riempiendo li vacui de lavori che s'vuole, et a un fornelletto fatto di carboni grossi con alquanto di fiamme di legna et con uno mantachetto soffiandovi dentro savoiva et si fa sopra al lavoro vostro scorrere collocandolo alquanto con uno legnetto o ferro quando e scorso, et si cava et lassa freddare. Dipoi cosi fatto con una lima levando el superfluo si senopre, et con una poca di camra et pomice sottile si pulisce, et con la terra di tripoli fregandolo si fa lucido et bello."—(P. 135.) The Pirotechnia was a second time printed at Venice, A. D. 1550, with the original wood-cuts, and some alterations in the orthography. A French translation appears to have been printed at Paris, A. D. 1572. The author is spoken of with commendation both by Agricola (in his preface), and Cardan (De Subtil). The former terms him an eloquent writer, which is true to a cer See also Brunet's Dict. Bibliographique, article Biringuccio. New Series, VOL. IV. 2 B 1 tain extent, though his eloquence, in spite of his origin, be not indeed of the purest Tuscan. I had almost forgotten to state, that Venoceio Biringuccio was a native of Sienna. I am, dear Sir, yours truly,, J. J. CONYBEARE. ARTICLE XII. ANALYSES OF BOOKS. Philosophical Transactions of the Royal Society of London, for 1822. Part I. WE have to apologize for so long delaying to analyze this part, which contains a series of papers of great importance; two of the most interesting, however, have already been inserted at length in the three preceding numbers of the Annals. I. The Bakerian Lecture.-An Account of Experiments to determine the Amount of the Dip of the Magnetic Needle in London, in August 1821; with Remarks on the Instruments which are usually employed in such Determinations. By Capt. Edward Sabine, of the Royal Regiment of Artillery, FRS. Capt. Sabine remarks, that the increased attention which has been given of late years to the subject of magnetism, and the consequent advance that has been made in the science, render it desirable that a greater degree of accuracy should be obtained, in the observation of its terrestrial phenomena, than has hitherto been the case. The instruments for ascertaining the dip of the 'needle, it is stated, have received little or no improvement during the last 50 years, and produce results, which, with every precaution, can be considered as approximate only. After describing the imperfections in the instruments alluded to, and explaining the errors which originate in them, the author proceeds to give an account of a dipping-needle, which he requested Mr. Dollond to make, on a construction suggested by Prof. Meyer, of Gottingen; as well as of the mode of observation therewith. "The needle is a parallelopipedon of eleven inches and a half in length, four-tenths in breadth, and onetwentieth in thickness; the ends are rounded; and a line marked on the face of the needle passing through the centre to the extremities, answers the purpose of an index. The cylindrical axis on which the needle revolves, is of bell metal, terminated, where it rests on the agate planes, by cylinders of less diameter; the finer these terminations are made, so long as they do not bend with the weight of the needle, the more accurate will be the oscillations; small grooves in the thicker part of the axis 2 receive the Y's, which raise and lower the needle on its supports, and ensure that the same parts of the axis rest in each observation on the planes. A small brass sphere traverses on a steel screw, inserted in the lower edge of the needle, as nearly as possible in the perpendicular to the index line passing through the axis of motion; by this mechanism, the centre of gravity of the needle, with the screw and sphere, may be made to fall more or less below the axis of motion, according as the sphere is screwed nearer or more distant from the needle, and according as spheres of greater or less diameter are employed. The object proposed in thus separating the centres of motion and gravity, is to give the needle a force arising from its own weight to assist that of magnetism in overcoming the inequalities of the axis, and thus to cause the needle to return, after oscillation, with more certainty to the same point of the divided limb than it would do were the centres strictly coincident." 1 "The centres of motion and of gravity not coinciding, the position which the needle assumes, when placed in the magnetic meridian, is not that of the dip: but the dip is deducible, by an easy calculation, from observations made with such a needle, according to the following directions: "If the needle has been carefully made, and the screw inserted truly as described," "two observations made in the magnetic meridian are sufficient for the determination of the dip, the two faces of the needle being successively towards the observers, renewing the position of the axis on its supports in such a manner that the edge of the needle which is uppermost in the one observation becomes lowermost in the other; the angles which the needle makes with the vertical in these two positions being read, the mean of the tangents of those angles is the co-tangent of the dip. But when needles are used in which this adjustment has not been made, or where its accuracy cannot be relied on, four observations are required; two being those which are already directed; the two others are similar to them, but with the poles of the needle reversed; calling then the first arcs F and f, and those with the poles reversed G and g, and taking 7 JA, D B+D 1 + B.C B+D = tang. F+tan.f =A = twice the co-tangent of the dip." "The instrument in which the needle was tried is already described in the Philosophical Transactions for 1819, p. 132, and several improvements which have since been added, in the Appendix to Capt. Parry's Voyages of Discovery, pp. 107, 159, &c. اور The experiments were made in the nursery-garden in the [NOV! Regent's Park, by permission of Mr. Jenkins the broo The situation is in all respects an eligible one, being far removed from the neighbourhood of iron." dood vis "The results by three different methods collected into one view, are as follow, viz. By 10 experiments with Meyer's needle. 0216 P of the By the times of vertical and horizontal oscillation. 70 "Whence 70° 03′ may be considered as the mean dip needle towards the north in the Regent's Park, in August and September, 1821, within four hours of noon, being the limit within which all the experiments were made." As the observations of Mr. Nairne in 1772, and of Mr. Cavendish in 1776, give an approximation of 72° 25′ for the dip in 1774, we obtain, it is stated, 3-02′ as the mean annual rate of diminution between, 1774 and 1821; and if we take Mr. Whiston's determination of the dip in 1720, 75° 10′, we obtain between the years 1720 and 1774, an annual diminution of 3.05'. Capt. Sabine says, "in conclusion, there appears reason to presume, from the preceding experiments, that the dip itself may be determined by Meyer's needle within a much smaller limit of uncertainty than has hitherto been the case by needles of the usual construction." II. Some Positions respecting the Influence of the Voltaic Battery in obviating the Effects of the Division of the Eighth Pair of Nerves. Drawn up by A. P. Wilson Philip, MD. FRS. Edin. (Communicated by B. C. Brodie, Esq. FRS.) This short paper appears to establish two momentous and novel facts in physiology; we shall give the principal results of Dr. Philip's investigation in his own words, distinguishing the important circumstances by the italic character. In some experiments in which the nerves of the eighth pair were divided in the neck of a rabbit, and the ends not displaced, and the animal was allowed to live some hours, it was found that food swallowed immediately before the division of the nerves, was considerably digested, even when the divided ends of the nerves had retracted to the distance of a quarter of an inch from each other." "In other experiments in which, after the division of the away from each other, little or no perfectly digested food, when the animal was allowed to live some hours, was found in the stomach; and the longer the animal lived, the smaller was the proportion of digested food found in the stomach; the great mass having the appear ance of masticated food, which, was not sensibly lessened in quantity, however long the animal lived. In an experiment in nerves, the divided ends had been turned hom which, under such circumstances, the stomach was exposed, from the time of the division of the nerves, to the influence of a voltaic battery sent through the lower portion of the divided nerves, its contents were apparently as much changed as they would have been in the same time in the healthy animal. The change was also of the same kind, the contents of the stomach assuming a dark colour, and those of the pyloric end being more uniform, and of a firmer consistence than those of the central and cardiac portions of the stomach; while the whole contents became less in quantity." III. On some Alvine Concretions found in the Colon of a Young Man in Lancashire, after Death. By J. G. Children, Esq. FRS. &c. &c. (Communicated by the Society for Promoting Animal Chemistry.) An abstract of this paper has already been given in the Annals for January last, p. 75, but we may add the following particulars: The concretions were found lodged in the arch of the colon, the coats of which were much thickened and formed into a sort of pouch, where they lay. The peritoneum was but little inflamed, the other viscera were healthy. The unfortunate subject of the paper never took a single repast without oatmeal in some shape or other, and the concretions consist of alternating concentric layers of a velvety fibrous substance from the inner coat enveloping the farina of the oat, and of phosphate of lime, together with the ammoniaco-magnesian phosphate. 1. IV. On the Concentric Adjustment of a Triple Object Glass. By William Hyde Wollaston, MD, VPRS. Dr. Wollaston here describes a method of correcting the central adjustment of a triple object-glass which appears not to have been used for that purpose, but for the details of which we must refer our readers to the paper itself, as they would be useless without the accompanying plate. The principle and its result are explained as follows: "When any bright object is viewed through a glass of this construction, without an eye-glass, there may be observed at the same time with the refracted image, a series of fainter images, that are found by two reflections from the different surfaces; and as the position of each of these images is dependent on the curvatures of that pair of surfaces by which it is formed, they appear at different distances from the object glass. Since the number of surfaces is six, the number of binary combinations of sis these surfaces is 15; and just so many images formed by reflection may be discerned. It is manifest, that if the glasses be duly adjusted to each other, so that their axes are correctly coinci dent, then this series of images must be all situated in the same straight line; and conversely, that any defective position may be immediately detected by a derangement of the line of images. ufpider boot By these guides alone, I have now so repeatedly restored |