In an experimental inquiry into the action of water on lead, published by me in 1829, in continuation of some previous researches by Guyton-Morveau, it was stated as the general result, that all very pure waters, such as distilled water, rain, and melted snow, act upon lead,—dissolving a trace of it, and causing the formation of an insoluble carbonate of lead in large quantity. It was like-wise shewn, that this action is prevented by the existence of neutral salts in solution; so that most terrestrial waters, as they contain saline matter, act feebly and only in circumstances favourable in other respects. Farther, it appeared to flow from comparative experiments, that this preventive power depends upon the acids of the salts, and not upon their bases;—and that their energy as preventives, that is, the minuteness of the proportion required to annihilate the action, is in the ratio of the insolubility of the compounds which the acids of the salts are capable of forming with oxide of lead.

1. On the 2d September 1839, M. Arago communicated to the Academy of Sciences of Paris a letter by M. Melloni, containing some very interesting experiments on the transmission of Radiant Heat. M. Melloni finds that rock-salt (which is well known to transmit rays of heat from all sources yet tried with equal facility) acquires, by being smoked, the power of transmitting most easily heat of low temperature, or that kind of heat which is stopped in greatest proportion by glass, alum, and (according to M. Melloni) every other substance.

I am not aware that this property has yet been known to belong to these substances; they are commonly considered and spoken of as opaque, without any qualification.

It was in examining the charcoal of the pith of the elder, that I was first led to entertain doubt of the accuracy of the current opinion.

The pith of the elder consists of polyhedral cells, commonly pentagonal, of from about to inch in diameter, formed of woody matter of extraordinary fineness, as may be inferred from their transparency when seen under the microscope, and their great lightness. They are unaltered in form, when converted into charcoal. The charcoal obtained (that which I examined was from a shoot of this year gathered in December) was brilliant, as might be expected, from its consisting of plates, and very soft and brittle; in other respects, in mass, it was nowise peculiar, having the ordinary colour and opacity of charcoal. When broken up, however, and seen with a high magnifying power, the detached plates were found to be transparent in different degrees (allowing lines drawn on the glass-support to be seen under them), and of different shades of brown—passing into black on one hand, and into almost white on the other, especially as seen by reflected light. In general appearance they were not unlike mica viewed with the naked eye. No pores were visible in them; but in some there were foramina, circular, or oval, varying in diameter from about of an inch to . The plates themselves varied in size from about to of an inch, estimating their width, and selecting the most entire. So thin were they, that, under a glass magnifying 800 diameters, the most transparent had no apparent thickness; the darker, less transparent, may have had a thickness of from about to of an inch, judging from one, the edge of which, when floating in water, was so inclined as to offer a tolerable view of it.

Although many proposals have been made to obtain a series of hourly meteorological observations by mechanical means, this desideratum has not, from various causes, been completely attained. The chief obstacle to be overcome, in such self-registering instruments, is the great amount of friction, which necessarily vitiates all the results, more especially in delicate instruments, such as the barometer and thermometer.

Dr Robert Hooke was the first to propose a self-registered series of meteorological observations, by an instrument, which he quaintly called a Weather-wiser; but no further notice is taken of this contrivance than a short description in one of his tracts, bearing the date 5th December 1678, which would lead us to believe that the instrument was never used. The late Alexander Keith, Esq. of Ravelston also proposed a similar contrivance, a description of which is contained in this Society's Transactions, Vol. 4th. This contrivance, from the constant friction excited by the marker on the revolving paper, seems likewise to have been abandoned.

The history of the habits and development of the salmon has been for ages a subject of dispute, even among men of science and experience. The general theory which prevailed regarding its earlier stage of existence was, that the spawn deposited in the autumn or beginning of winter, produced by development the smolts which were seen descending to the sea in the course of the next ensuing spring.

In regard to its after state, some supposed that the smolts which descended the rivers in spring or early summer returned as grilses that same season. Many doubted this theory, and maintained that it was impossible, or very improbable, that they should return so speedily in that greatly enlarged condition; their only argument, however, being founded on the unlikelihood of such a rapid growth.

In 1836, I communicated to this Society the results of an extensive series of observations on Terrestrial Magnetic Intensity, made with the Hansteen Apparatus, which is the property of the Society. Some results with a small Dipping Needle, belonging to myself, were also given, but without great confidence in their accuracy.

I held then, however, the opinion which I still do, and to which the remarkable geometrical researches of Professor Gauss of Göttingen on Terrestrial Magnetism have given additional weight, that the element of horizontal intensity ought to be determined, and its laws of variation, in the first place, ascertained, independent of any other. Even should the deduction of total intensity be the sole ultimate object, I hold that an observer with only portable, and consequently imperfect instruments at his command, would do well to separate completely his investigations as to horizontal intensity from those upon dip, and then, by the skilful grouping of each set, having obtained a law of variation of each element according to the co-ordinates of Latitude and Longitude, the two partial results may be combined into the general one of total intensity , whilst either series may be used to check future observations, or be combined with any single future series in which one of the elements should be better determined.

That the eggs of numerous parasitic animals may be deposited in the textures of living beings, and that these develop themselves in such textures, and draw thence their nourishment, has been long known. But that, under particular circumstances, certain cryptogamic plants are capable of germinating and fructifying in the living tissues of animals, and especially in man himself, is a discovery of recent date.

In certain investigations which I have presented to the Society, relative to the modifications which light undergoes when it meets with a medium more dense than that in which it is travelling, the law of force has been supposed to be that of the inverse square of the distance. On re-examination of this subject, I find that there is no necessity for restricting the computations by the hypothesis of any particular law. The conclusions are perfectly independent of the law, provided one of the equations of reduction, the value of which it is not possible to compute by any known methods of analysis, be admitted as an experimental result. The object of the present Memoir is twofold : 1st, To present the analysis of the general theorem of vibrations at the surface of an interrupted medium in its most simple form; and, 2d, To apply the results to the case of reflection unaccompanied by refraction.

This remarkable seed or nut is now well known in London, as a substance extensively carved into a variety of ornaments, and capable of receiving as high a polish as the finest ivory; which it also greatly resembles in colour. I lately obtained various specimens both of the nut in its natural state and of the fine turnings produced in the process of working it, being desirous of submitting them to a chemical examination.

The nuts in my possession vary in size from a pigeon's to a hen's egg, and have a somewhat angular shape. They are covered with a brown epidermis, and have an outer shell of an inch thick, and consisting of an outer white and an inner brown layer. The inner mass of the nut is remarkably close grained and homogeneous to the naked eye; and when cut and polished exactly resembles animal ivory. The hardness is considerable; the white mass yielding with some difficulty to a knife. Thin portions are translucent. The density of the white mass is 1.376, at 53° F.

The present Memoir is, to a certain extent, a continuation of one which the author presented to the Society in December 1838, and which has since been published in the thirteenth volume of the Transactions. Other motives, however, than the desire of completing the subject, have influenced him in producing the following analysis. A very important point in the hypothetical conditions which Fresnel assumed to hold with respect to polarized light, has, of late, been warmly combated in various quarters. Fresnel supposed that light polarized in a given plane consists of vibrations of such a nature that the motion is perpendicular to that plane. Neumann and other writers contend that the very opposite is the fact. We hope to be able to offer evidence of some little weight in favour of the former view; at the same time we do not pretend to shew the actual impossibility of the truth of the latter.

In the course of an examination of Bishop Berkeley's “New Theory of Vision,” the foundation of the Ideal Philosophy, I have found it necessary to repeat many old experiments, and to make many new ones, in reference to the functions of the eye as an optical instrument. I had imagined that many points in the physiology of vision were irrevocably fixed, and placed beyond the reach of controversy; but though this supposition may still be true in the estimation of that very limited class of philosophers who have really studied the subject, yet it is mortifying to find that the laws of vision, as established by experiment and observation, are as little understood as they were in the days of Locke and Berkeley. Metaphysicians and physiologists have combined their efforts in substituting unfounded speculation for physical truth; and even substantial discoveries have been prematurely placed in opposition to opinions of which they are the necessary result.

Malpighi was the first to announce that all secreting glands are essentially composed of tubes, with blind extremities. Müller, by his laborious researches, has brought this department of the anatomy of glands to its present comparatively perfect condition. Purkinje announced his hypothesis of the secreting function of the nucleated epithelium of the gland ducts, but made no statement to shew that he had verified it by observation. Schwann suggested that the epithelium of the mucous membranes might be the secreting organ of these surfaces. Henle described minutely the epithelium cells which line the ducts of the principal glands and follicles, but did not prove that these are the secreting organs. The same anatomist has stated, that the terminal extremities of certain gland ducts are closed vesicles, within which the secretion is formed, and which contain nucleated cells. Henle has not, therefore, verified the hypothesis of Purkinje, although he is correct in stating that the terminal vesicles of certain gland ducts are closed. It will be shewn, in the course of this paper, that the secretion is not formed, as Henle has asserted, in the closed vesicles, but in the nucleated cells themselves.

Although the sea-trout (Salmo trutta) cannot be considered either of so much importance to the community as an article of food, or so interesting in its habits and economy to the naturalist as the true salmon, nevertheless, it is universally allowed to rank next in value to that species. It holds a high place in the estimation of the public as an article of diet, and is, consequently, an object of great commercial value to our fisheries. Its history being still almost as involved and obscure as was that of the salmon some seasons back, I am induced to offer the following remarks with a view to its elucidation.

To all those who have paid any attention to the subject of quarantine, it is well known that certain articles are held to be susceptible of conveying the contagion of plague; that certain others, in regard to this property, are considered doubtful; and that others are held to be unsusceptible of retaining and communicating it.

Are these distinctions accurate? Are they founded on well-established facts? On these questions I shall have the honour of submitting some remarks to the Society, with the hope of drawing attention to a subject of much importance, and hitherto, in a scientific point of view, strangely neglected.

It has been justly observed that the great discovery of the appropriation of the different portions of the Nervous System to the exercise of different functions, would never have been clearly established, but for the fortunate circumstance that, in certain parts of the body, especially on the face, the nerves of sense and of voluntary motion are distinct throughout their whole course. And this consideration may instruct us that, when we have an organ supplied with a variety of nerves, known to be of perfectly different endowments, the study of the peculiarities of these nerves may give us an insight into the purpose or use of some of those pieces of structure in all parts of the Nervous System, in which we must still admit that we see much contrivance, without understanding its intention.

The object of the following paper is to lay before the Royal Society the results of a repetition of several of Dr Samuel Brown's processes for the conversion of carbon into silicon. The greater number of these processes were published in the Society's Transactions for 1840–41; and certain additional ones have since appeared in a separate form. The latter were much simpler, and more readily performed, than those made public at an earlier period; and to one of these we first directed our attention.

The Acephalocyst, or simple Hydatid, is composed of a vesicle, containing a watery fluid, which, in the normal state of the creature, is quite transparent and colourless (Pl. XIV., fig. 1.) The internal surface of the vesicle is generally studded with numerous cells of various sizes, many of which are found detached and floating loose in the fluid contained in the vesicle. These are the young Hydatids. Their development will be described when we come to that portion of the present paper, which has been set apart for that purpose.

It is well known to those who have paid attention to the progress of Fossil Ichthyology that, until the publication of M. Agassiz, the distinctive characters of the orders, genera, and species of Fossil Fishes were but imperfectly understood. Vague analogies were relied on to connect them with the types of living genera, and the looseness of the received specific characters rendered it difficult for the geologist to determine whether the specimens he collected were previously recognised, or still nondescript. It is obvious that useful characters of fossil species are chiefly to be obtained from those portions of their structure least subject to alteration from decay; and as the exterior scaly envelopes of the primeval fishes are usually the portions best preserved and most easily recognised in their rocky sepulchres, M. Agassiz was naturally led to study these with minute attention. This acute observer speedily discovered that, in the form and connections of the scales, he had a general character which would enable him to connect into very natural groups, species differing from each other in size and form. On this basis he has established his four Orders of Fossil Fishes—the Ganoidei, the Placoidei, the Ctenoidei, and the Cyclodei—divisions named from the appearance of the scales.

The subject of the following Memoir has been already touched on in a communication which I made to the Cambridge Philosophical Society, and which appears in the seventh volume of their Transactions, Art. IX. For the better understanding of what follows, it is desirable to state briefly the contents of that paper. Its object is to estimate the quantity of light which is received on a screen of unlimited dimensions, after passing through a certain aperture, or suffering reflection at two mirrors, as in the case of the interference experiment, so as to exhibit the appearance of bands.

Although some of the phenomena of Muscæ volitantes may be seen by persons of all ages, and with the best eyes; and though those which are more peculiarly entitled to the name are exceedingly common beyond the middle period of life; yet no account has been given of them that has even the slightest pretension to accuracy. M. De La Hire, in his Differens accidens de la Vue, describes these Muscæ as of two kinds; some permanent and fixed, which he ascribes to small drops of extravasated blood upon the retina; and others, as flying about, and changing their place, even though the eye be fixed. The first kind, he describes as like a dark spot upon a white ground; and the second, as like the knots of a deal board. Some parts of them, he says, are very clear, and surrounded with dark threads, and are accompanied with long fillets of irregular shapes, which are bright in the middle, and terminated on each side by parallel black threads.