wards towards the ciliary ligament. They arise at the pupillary edge, each by two or three fine twigs, which quickly meet in a common trunk, or sometimes run separately as far as the outer half of the iris, where they unite in a common trunk. The deep layer consists almost entirely of a fine network belonging to the radiating muscular fibres, and presenting a close analogy with the fine vessels supplying striated muscular fibre; the vessels being very minute, and the meshes elongated in the direction of the fibres. Sometimes the vessels from this layer unite into a small ramuscule, which empties into a radiating vein; at others they unite in a common trunk, passing beneath the ciliary ligament into the choroid. The movement of the blood in the veins is generally not too rapid to distinguish the direction of the current and the separate globules, which appear to be constantly springing from around the edge of the pupil and pouring outwards along the veins of the iris into the choroidal and ciliary vessels. When the pupil is contracted, the radiating vessels are rectilinear; but when it dilates they become curved and bent into zigzag and spiral forms, which are more or less curved or obtuse in proportion to the degree of dilatation of the pupil. This change in the form of the vessels does not appear to produce any difference in the speed of the current of blood. Around the ciliary ligament are two and often three circular vessels, receiving the blood from the conjunctiva of the cornea and sclerotic, partly from the iris, and probably from the ciliary processes. Two of them are venous, and empty themselves into four large veins, corresponding to the anterior ciliaries, which arise in a perpendicular direction, and after following a rectilinear course over the sclerotic, finally end in the ophthalmic vein. The third circular ciliary vessel is of an arterial nature, as shown by the greater thickness of its parietes and the rapidity of its current. The current of blood in these vascular circles is a most interesting object from the variety of its course, as into each anterior ciliary vein the blood is seen pouring out from the circular vein in two opposite currents, to be united into one in the larger vessel. The author also describes the appearance presented by the blood poured into the circular veins by their afferent vessels. II. "Researches on the Action of certain parts of the Solar Communicated by Dr. SHARPEY, Scc. R.S. Received In 1847 I discovered that light has the power of acting directly upon the iris so as to produce there a muscular contraction, manifesting itself by the constriction of the pupil. If an eye taken out from the orbit is alternately exposed to light and darkness, we find that the pupil becomes alternately constricted and dilated*. It was interesting to know whether the stimulation of the muscular fibres of the iris is produced by the chemical power of light or not. I had already found, in 1847, that only the parts of light which seem to have but very little chemical action, have the power of exciting contractions in the iris. But my experiments having been made with light passing through coloured glasses, were not decisive. Lately I have performed many other experiments in making use of light decomposed by the prism. In one case, with the assistance of Messrs. Dubosc and Nachet, jun., I experimented with electric light, and in the other cases I made use of direct solar light. In all these cases the same results have been obtained. I uniformly found that the yellow part of the spectrum acted as well as undecomposed light, and that the other parts of the spectrum had either no action at all, or only a very slight one. The parts of the green and orange adjoining the yellow had a decided but very slow action. The two extremities of the spectrum, and the dark places in their neighbourhood, not only had no constrictive action upon the pupil, but did not prevent it from dilating, and the dilatation seemed to take place as quickly as when the eye was put in complete darkness. From these experiments it appears that the power possessed by light, of stimulating the circular fibres of the iris, belongs not to its chemical or to its calorific parts, but to its illuminating elements. Comptes Rendus de l'Acad. des Sciences, vol. xxv. pp. 482 & 508 ; and Comptes Rendus de la Société de Biologie, vol. i. p. 40. It seems therefore that it is not by a chemical action, but by a peculiar dynamical influence that light produces contraction of the iris. The power of the iris to contract when stimulated by light lasts extremely long, particularly in certain animals. In the eel I have found the muscular irritability of the iris, in one case, lasting sixteen days, during the last winter, in eyes taken out from the orbit. This is an interesting fact, not only on account of the long duration of vitality in the iris, but on account of the conclusion that we are entitled to draw from it, that muscular fibres may be stimulated without the intervention of nerves. In the iris of the eel the nervefibres are found very much altered a few days after the extirpation of the eye from the orbit, and they are almost destroyed twelve or fifteen days after this extirpation, i. e. at a time where muscular irritability is sometimes still existing. III. A paper was in part read, entitled "Photo-chemical Researches. Part I. On the Measurement of the Chemical Action of Light." By Professor BUNSEN of Heidelberg, and HENRY ENFIELD ROSCOE, B.A., Ph.D. Communicated by Professor STOKES, Sec. R.S. Received November 12, 1856. November 27, 1856. Sir BENJAMIN C. BRODIE, Bart., V.P., in the Chair. Dr. Noad was admitted into the Society. In accordance with the Statutes, notice was given of the ensuing Anniversary Meeting, and the following names of persons recommended for election as Council and Officers for the ensuing year, were announced from the Chair : President.-The Lord Wrottesley, M.A. Treasurer.-Major-General Edward Sabine, R.A., D.C.L. Secretaries. William Sharpey, M.D. George Gabriel Stokes, Esq., M.A., D.C.L. Foreign Secretary.-William Hallows Miller, Esq., M.A. Other Members of the Council.-James Moncrieff Arnott, Esq.; William Benjamin Carpenter, M.D.; Arthur Cayley, Esq.; The Very Rev. The Dean of Ely; William Fairbairn, Esq.; Arthur Farre, M.D.; William Robert Grove, Esq., M.A.; Joseph Dalton Hooker, M.D.; William Hopkins, Esq., M.A.; William Allen Miller, M.D.; Lyon Playfair, Esq., C.B., Ph.D.; Rev. Bartholomew Price, M.A.; Sir James Clark Ross, Capt. R.N., D.C.L.; Rear-Admiral W. H. Smyth, D.C.L.; John Stenhouse, LL.D.; John Tyndall, Esq., Ph.D. Mr. Grove, Dr. Hooker, Mr. Hopkins, Sir James C. Ross, and Dr. Tyndall were elected Auditors of the Treasurer's Accounts on the part of the Society. The reading of Professor BUNSEN and Dr. HENRY ROSCOE'S Paper "On the Measurement of the Chemical Action of Light," was resumed and concluded. (Abstract.) The only instrument which has been applied to the measurement of the chemical action of light was proposed in 1843 by Dr. Draper of New York. The sensitive substance employed by him was a mixture of chlorine and hydrogen, and by measuring the diminution ensuing on exposure to light, he experimentally determined some important relations of photo-chemical action. Draper's instrument is, however, not adapted for accurate measurements, owing, in the first place, to the fact that the gas is subject to varying pressure; and, in the second place, that the statical equilibrium, which must exist between the free and dissolved gases, in order that the free gas should consist of equal volumes of chlorine and hydrogen, was never approached. In order to obtain more accurate results than was possible with Draper's tithonometer, we sought for means of preparing a gas containing equal volumes of chlorine and hydrogen; this means was found, notwithstanding Draper's contrary statement, in the ele ro lysis of strong aqueous hydrochloric acid. A series of volumetric analyses proved that the gas thus evolved consisted, as soon as the requisite saturation had been attained, of exactly equal volumes of its component parts, and did not contain the slightest trace of oxygen or oxides of chlorine. Another series of experiments with gas, similarly prepared, but allowed to stand before analysis for many hours in the dark in closed vessels, proved that, at the ordinary atmospheric temperature, the gases do not enter into combination when the light is excluded. Being thus enabled to prepare a substance which undergoes decomposition on exposure to light, but does not change on preservation in the dark, we proceeded to construct an apparatus by means of which the laws of the chemical action of light might be thoroughly investigated. After many fruitless attempts, we have succeeded in constructing an instrument, by which not only accurate comparative determinations can be made, but which has enabled us to reduce the chemical action of light to an absolute measure. The most essential conditions fulfilled by our instrument are the following: 1. A continuous evolution of a gas consisting of exactly equal volumes of chlorine and hydrogen free from all foreign impurities. 2. Constant pressure on the gas and liquids throughout the appa ratus. 3. Absence of all caoutchouc or other organic matter which might alter the composition of the gas. 4. Exclusion of all variation in the composition of the gas in the apparatus from exposing the saturated liquids to the light. 5. Complete establishment of the statical equilibrium between the free and dissolved gases. 6. Elimination of the disturbing action of radiant heat. The instrument in which these conditions are fulfilled is constructed entirely of glass, and consists essentially of four parts, viz.— 1, a decomposing tube in which the gases are generated from carbon poles; 2, a washing tube containing water, furnished with an airtight glass stopcock; 3, the vessel in which the gases are exposed to the action of the light attached to the other parts of the apparatus by air-tight ground-glass joints; and 4, a horizontal tube on which the diminution of volume in the insolation vessel is observed by means of a millimeter scale. |