By the discovery of the different refrangibility of light, Sir Isaac Newton laid open the true cause of the principal imperfection of refracting telescopes; and having inferred from the experiments which he made, that the refraction of the different rays composing the prismatic spectrum, was always in a given ratio to the refraction of the mean refrangible ray, this great philosopher was led to conclude, that the imperfection which he had discovered in dioptrical instruments was without remedy.

Since reading the paper upon the theory of the earth, I have been employed in examining many parts of this country, in order to enquire into the natural history of granite. In this undertaking, I have succeeded beyond my most flattering expectations; and I am now to communicate to this Society the result of my observations.

In the paper just referred to, it was maintained, from many different arguments, that all the solid strata of the earth had been consolidated by means of subterraneous heat, softening the hard materials of those bodies; and that in many places, those consolidated strata had been broken and invaded by huge masses of fluid matter similar to lava, but, for the most part, perfectly distinguishable from it. Granite also was considered there as a body which had been certainly consolidated by heat; and which had, at least in some parts, been in the state of perfect fusion, and certain specimens were produced, from which I drew an argument in support of this conclusion.

No quality is more inconsistent with the character of a stone than flexibility. A flexible stone, therefore, presents an idea which naturally strikes us with surprise. For though among mineral bodies, we find flexible substances of the stony kind, such as mica, mountain leather, and amianthus, these minerals owe their flexibility, either to their thinness, or to the fibrous structure of their parts. Therefore, when a stone of any considerable thickness is said to have flexibility, we are led to think that here is something very extraordinary; and we wish to know upon what depends that quality, nowise proper to a stone.

Sir Joseph Banks, to whose indefatigable ardour for the advancement of natural history, the philosophical world is so much indebted, made a voyage to Iceland in the year 1772, to enquire into the productions of that remote part of the world, and particularly into those of its famous volcano. When he returned, he brought from thence, among many other natural productions, some petrified vegetables, and incrustations, formed by the waters of the boiling springs; and he was so good as to present a part of them to his friends here, who were surprised to find them composed of siliceous earth. As this was the first example observed, of water containing this earth in such quantity as to form siliceous petrifactions, it raised a strong desire to have an opportunity of examining the water, and of learning by what means this siliceous matter was dissolved in it; and this opportunity was at last given us by John Thomas Stanley, Esq; who, excited by motives similar to those of Sir Joseph Banks, equipped likewise a vessel, and made a voyage to Iceland, during the summer 1789.

Dear Sir,

I have been prevented hitherto, by various occupations, from acquitting myself of a promise you received from me, (I am ashamed to think how long a time since), that I would send you an account of the hot springs in Iceland, from whence the water was brought which you have lately analysed. I have trusted you would excuse a delay not altogether voluntary. It will be now my endeavour to gratify your curiosity as far as I am able; and to acquaint you with every particular, as well concerning the springs as the country near them, which I think you may find in the least interesting.

Dear Sir,

Part of my promise has been accomplished in a former letter, in which I gave you the fullest account I could of the springs of boiling water that rise in the valley of Rykum. It now remains for me to send you a description of those we visited in the neighbourhood of Haukadal.

These last are the most remarkable in the island, and the eruptions of water from some of them so astonishing, that I doubt whether any adequate idea of their effect can be given by description. Abler pens than mine might fail probably in attempting to do justice to such wonderful phenomena. The objects, however, are so highly interesting in themselves, that even the simplest narrative that can be given of them will be read with more than ordinary attention.

The restoration of the ancient books of geometry would have been impossible, without the coincidence of two circumstances, of which, though the one is purely accidental, the other is essentially connected with the nature of the mathematical sciences. The first of these circumstances is the preservation of a short abstract of those books, drawn up by Pappus Alexandrinus, together with a series of such lemmata, as he judged useful to facilitate the study of them. The second is, the necessary connection that takes place among the objects of every mathematical work, which, by excluding whatever is arbitrary, makes it possible to determine the whole course of an investigation, when only a few points in it are known. From the union of these circumstances, mathematics has enjoyed an advantage of which no other branch of knowledge can partake; and while the critic or the historian has only been able to lament the fate of those books of Livy and Tacitus which are lost, the geometer has had the high satisfaction to behold the works of Euclid and Apollonius reviving under his hands.

The Quassia Polygama has long been known in Jamaica, and in fome other islands in the West Indies, not only as an exexcellent timber, but as an useful medicine in putrid fevers and, fluxes. With us, it is called Bitter-wood, and in the Windward Islands, the Bitter Ash. The bark has for some time been prescribed by practitioners here, and exported to England in considerable quantities, for the purposes of the brewers of ale and porter. On these accounts, a fuller description of this plant than has hitherto appeared, will be acceptable to the botanist and the public at large.

This monster, of which the mother was delivered by Mr Thomas Anderson, surgeon in Leith, after the birth of a complete child at the full time, had its proper membranes and a placenta, with a short umbilical cord.

The following parts were wanting in it; to wit, the bones of the head; the brain, with the organs of sight, hearing, smell and taste; the neck; about one half of the ribs; the larynx, trachea and lungs; the heart; the pharynx, œsophagus and stomach, with all the small intestines, except the end of the ilium; the anus; the liver, spleen, pancreas and omenta; the renal glands; terminations of the ureters; the middle part of the urethra; the right testicle; both arms; both patellæ; with several of the bones of the feet and toes.

On the 3d of November last, Sir James Hall and Dr Rutherford asked me to repeat with them some experiments on what has been called Animal Electricity, which were first performed by Dr Galvani, Professor of Anatomy at Bologna, and of which an account had been communicated by Mr Seguin of Paris to Dr Black, in a letter dated Paris, 3d August.