My first precise views of the structure of the Tunicata were formed by the perusal of Mr Huxley's masterly papers dealing with the anatomy of Salpa, Pyrosoma, Doliolum, and Appendicularia, in the Phil. Trans. for 1851, Part II.; and I have since had abundant opportunity of verifying all the important facts, made known by that original observer, in the papers to which I have alluded.

Having thus acknowledged my guide in this field of research, I can scarcely claim much originality as relates to pure anatomy; but I hope that the method here adopted, in opening up this interesting subject, will be found in keeping with nature, as it is the result of much study and practical investigation.

Great credit is due to those observers who have been enabled to give to science both clear and comprehensive views of the anatomy of creatures which have only been presented to them in a spirit-preserved, opaque, brittle, and contracted state; for it is certain that their penetration in this respect could not be successfully brought into exercise without the aid of much knowledge, both bibliographical and practical. Yet there are many whole animals, and, in particular, parts of animals, which must be seen in the living state, to be at all comprehended by even the most brilliant mind; and this fact has induced me to make drawings and notes of many interesting matters connected with the pelagic mollusca, when the living animals fell casually under my own observation. In the present communication, however, I shall confine myself to the genus Clio.

In a successful haul of the towing net, off the Island of Sardinia, I obtained a very beautiful Firola, which gave me a good opportunity of testing the truth of my former conclusions with regard to the economy of the Heteropoda in general, and of Firola in particular; and I have great pleasure in submitting the facts arrived at, with the accompanying enlarged figure of the visceral nucleus and the neighbouring parts, to the Royal Society of Edinburgh, as an appendix to my paper “On the Anatomy and Classification of the Heteropoda,” already brought under its consideration.

The disintegration of solid bodies by means of active or feeble solvents, or by those invisible processes which go on during long periods of time, has, so far as I know, been studied neither by the chemist nor the natural philosopher. In 1837 I submitted to this Society a paper “On the Optical Figures produced by the Disintegrated Surfaces of Crystals,” containing experiments which I believe have not been repeated, and results which no person has attempted to explain. Since that paper was published, my attention was called to the structure and properties of decomposed glass, in consequence of having had occasion to study the action of its coloured films, in absorbing definite parts of the spectrum.

The laws of the polarisation of light when reflected from the surfaces of solids and fluids, and when refracted and transmitted by translucent and transparent bodies, have been successfully investigated; but no experiments, I believe, have been made on the polarisation of light by rough or unpolished surfaces, such as ground glass, painted surfaces, pounded glass, snow, white powders, and solids and fluids reflecting white light from their interior. When studying the polarisation of the atmosphere, and anxious to discover the cause of its partial polarisation, and of the three neutral points or spots, in which there is no polarisation, I investigated the action of rough surfaces upon light, under the conviction that the sky or atmosphere was a rough surface like any aggregation of white or coloured particles. Had the atmosphere been specular like water or any body with a polished surface, the image of the sun would have been seen in it by reflexion, but being composed of aerial and aqueous molecules, it must reflect the sun's rays like pounded glass, or any white or coloured powders.

During the last half century, observations on the polarisation of the atmosphere were made by several eminent observers—by Arago, Delezenne, Babinet, and Zantedeschi; but no result of special importance was obtained till Arago made the great discovery that there existed in the atmosphere a point, or spot, in which there is no polarisation. At sunrise or sunset he found that this neutral point was 20° or 30° above the point opposite to the sun, or what we may call the Antisolar point. The name of Arago's neutral point has been given to this spot without polarisation. It is best seen after sunset. At St Andrews it is above the horizon all the day, between the middle of November and the end of January.

While engaged last autumn in examining with a hand-lens the contents of a phial into which I had transferred some of the refuse of the dredging-boats employed in the oyster fishery on the coast of South Devon, my attention was attracted by a minute organism which adhered to a fragment of one of the larger Sertularidans. Under this low power it resembled somewhat a Campanularia, with the polype expanded; but, on being removed with a portion of the substance to which it was attached, and placed in a glass trough under the compound microscope, I found that it had closed up, and now resembled in form a cup surmounted by a pyramidal lid, and supported on the summit of a long jointed stem (Plate XIII., fig. 3).

In compliance with the desire which the Council have done me the honour to express, I have drawn up the following account of the recent progress and present state of Sanskrit studies, prefixing such an outline of the earlier history of these researches as may serve to complete the review, and render it more easily intelligible.

In this sketch I do not profess to communicate anything new, but merely seek to present such a summary of the results already obtained, as may convey to those who have not bestowed any special attention on the subject some idea of the character and affinities of the Sanskrit language, and of the nature and contents of Indian literature, as well as of the advances which have of late years been made in the principal branches of the study.

Before proceeding to the subject of this paper, I wish to advert to the following well-known theorem.

Let ABC be any triangle with its inscribed and circumscribed circles. Then if we take any other point D in the exterior circle, and draw the tangents DE, EF, FD, the last tangent will come again to the original point D. A similar theorem is true of a polygon of any number of sides which is both inscribed in, and circumscribed to, a circle. Also if ellipses are substituted for circles. Of these theorems I remember to have seen a demonstration founded on the theory of elliptic integrals. But this appears to me to be a great waste of analytic power; for the theorem really results from first principles, as I think will be manifest from the following considerations.

The subject to which I have to invite the attention of the Society this evening is one of no modern origin, the name of Hippocrates, amongst others of the fathers of medicine, being commonly associated with it. There is, indeed, perhaps no branch of medical inquiry whose history dips more deeply into the obscure pages of antiquity. The influence of weather upon disease and mortality has been acknowledged as a potent external force in every age, from that eminently speculative and credulous period when physicians professed to receive their diagnostic as well as their therapeutic inspirations from the stars, down to our own day. And yet there is perhaps no question in the whole cycle of medical sciences which has made slower progress than the one we have now to consider. People believe that the weather affects them. They speak of its influence, sometimes commendingly, more frequently with censure, on the most trivial occasions; but beyond a few commonplace ideas, the result of careless observation, or perhaps acquired only traditionally, they seldom seek a closer acquaintance with the subject. Our language teems with medico-meteorological apophthegms, but they are notoriously vague. The words which are most commonly employed to signify the state of the weather at any given time, possess a value relative only to the sensations of the individual uttering them. The general and convertible terms—bitter, raw, cold, severe, bleak, inclement, or fine and bracing, convey no definite idea of the condition of the weather; nay, it is quite possible that we may hear these several expressions used by different persons with reference to the weather of one and the same place and point of time. In order, then, to render medico-meteorological researches more trustworthy, we must be careful to employ, in the expression of facts, such symbols only as have a corresponding value in every nation.

In the construction of the animal kingdom, Nature shows herself always provident and saving, both in the amount of organic matter which she uses, and in the complexity of the organic structures which she moulds out of that matter. She never employs any superfluous quantity of material, nor any superfluous quality of mechanism. If a low type of structure in an organ is sufficient for the due performance of the given function of that organ, she never resorts to a higher or more complex type. She does not build organs or animals with the higher organic types of nerves, capillaries, lymphatics, &c., when these organs or animals do not require for their function, or for their life, the special physiological action of nerves, capillaries, or lymphatics. She expends no unnecessary workmanship upon the vital machinery which she employs, nor does she ever add to it any unnecessary pieces of organic apparatus.

I have already endeavoured to prove that Auroræ and Earth-currents, far from producing magnetic disturbances by their direct action, are themselves only secondary or induced currents, generated by those small but abrupt changes of the earth's magnetism which constitute such disturbances. The proof of this statement was in the first place derived in a general manner from the fact that during the notable magnetic storm of August and September 1859, all the elements of the earth's magnetism at Kew remained for many hours on one side of their normal positions, while, on the other hand, the earth-currents observed during that time by Mr C. V. Walker had their direction reversed every two or three minutes.

The following pages contain an account of a few double-star measures which, by the kind permission of J. W. Grant, Esq., of Elchies, in Morayshire, I was enabled to make there in September 1862, with his large and equatorially mounted refracting telescope; and as that instrument is altogether the best and most powerful of its kind which has hitherto been erected in Scotland, such a trial of its capabilities, and the first which has been published, will undoubtedly have a peculiar interest for the Royal Society of Edinburgh.