In a paper which I had the honour of submitting to the Society, at the end of last session, I gave a detailed account of the effects of mechanical compression and dilatation, in communicating to glass and other uncrystallised bodies, all the properties of doubly refracting crystals. I had at that time attempted, without success, to alter the polarising structure of doubly refracting crystals, although I applied the force of powerful screws to Topaz, Rock-crystal, and Calcareous spar. All the specimens which I employed were crushed to pieces by the pressure, but exhibited no traces of the coloured rings when exposed to polarised light.

Some years ago I proposed, as decisive of the question which has been the subject of controversy on the nature of Oxymuriatic and Muriatic Acids, the experiment of procuring water from muriate of ammonia, formed by the combination of dry ammoniacal and muriatic acid gases. Muriatic acid gas being the sole product of the mutual action of oxymuriatic gas and hydrogen, it follows, that if oxymuriatic gas contain oxygen, muriatic acid gas must contain combined water; while, if the former be a simple body, the latter must be the real acid, free from water.

The Chloridic Theory, though more limited in its application to chemical phenomena, than the Antiphlogistic, may justly be regarded as of scarcely inferior importance. If established, it leads to the adoption of entirely new views concerning combustion and many of its products; it removes the muriates, a set of apparently well characterised saline bodies, from the class of salts altogether; and it has given birth, by analogy, to two new genera of compounds, in which iodine and fluorine, like chlorine, act a corresponding part with oxygen, in the system of Lavoisier.

In the Philosophical Transactions for 1816, I have described at great length the various phenomena which are exhibited by glass and other substances to which the property of double refraction has been communicated by heat, by rapid cooling, by evaporation, or by mechanical compression and dilatation. In pursuing the same subject, I have observed many singular facts respecting the developement of new axes, by a change in the form and condition of the plates; and by submitting the phenomena to accurate measurement, I have succeeded in determining the laws which regulate the distribution of the polarising force. A brief account of these results will form the subject of the following paper.

The obligations of Experimental Physics to the labours of Lord Bacon, have been largely acknowledged by the generality of those who have treated of the History of Modern Science; insomuch, that the title of Father of experimental Philosophy has been oftener conferred upon him than upon any other of its benefactors. There are some, however, who seem to think, that there is no good ground for honouring him with this title, either on account of the merits or the effects of his writings. They do not indeed deny, that his views as to the proper objects and method of philosophizing were extensive and just; but they contend, that he had no peculiar merit in having stated these views; that all that he taught was virtually and more effectually taught by the discoveries of some of his contemporaries; and that, in fact, there are no traces of his agency to be found in the discoveries that followed.

Nice is situated on the shore of the Mediterranean, in lat. 43° 41′ 16″ N. and long, east of Greenwich 7° 16′ 37″. The county of which Nice is the capital, was comprehended in the Roman province of the Maritime Alps: it was included, while under the influence of France, in a department to which the same name was given; and now, it is restored to the sovereignty of Piémont, it may be considered as bounded on the west by the Var, which separates it from France, on the north and east by the mountains of Dauphiné and Piémont, and on the south, it is washed by the Mediterranean.

The distribution of Heat over the surface of our Globe, is a capital object in the economy of Nature. The infusion of that active element communicates to bodies the principle of motion, and quickens the ceaseless revolution of the circle of generation and decay. But Heat, unlike air, water, or earth, appears never in a distinct and separate form: It exists onlv in a state of combination with other tangible substances; among which, it migrates from one to another. On the regulated tide of this transmission, depends the stability of the present order of things.

Having for a number of years been constantly moving about, in situations where I could not convey large astronomical instruments, I have repeatedly tried to what extent of accuracy and consistency I could arrive with the smaller ones. The results have convinced me, that a great deal of accuracy may in that way be obtained; and that the sextant is an instrument, which, if perfectly understood, would be in higher estimation, and more general use, than it is at present. The observations I am about to submit, were made with a ten inch sextant of Troughton's, divided on platina to 10″, (No 1200).

It is possible, that the following observations may contain little that is new to those who are familiarly acquainted with the details of the science of Hydrostatics. But as I have not met with any remarks on the subject, in the course of my limited reading, the experiments which were performed, and the conclusions to which they lead, are here submitted to the consideration of the Royal Society.

Alexander Tytler was born at Edinburgh, 15th October 1747. He was the eldest son of our late venerable associate William Tytler, Esq. of Woodhouselee, in the county of Mid-Lothian, and of Anne Craig, daughter of James Craig, Esq. of Costerton, in the same county.

If the most important education is that which is received beneath the paternal roof,—if it is there that the principles and tastes of future life are chiefly formed, the education of Mr Tytler began under fortunate auspices. His father was a man of high honour, of generous affections, of cultivated taste, and of distinguished eminence in his profession.