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.

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 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.

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.

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.

That the common varieties of wood which float in water, owe their apparent lightness to air contained in their structure, is generally admitted by those who have paid any attention to the subject. By means of the air-pump, the fact is clearly demonstrated. Under the exhausted receiver, after a certain time, the time varying with the quality of wood, all the different specimens which I have tried have sunk; I may mention two or three in particular, as examples. A piece of oak, weighing 29.7 grs., sank in distilled water, after having been subjected to the air-pump three days;—a piece of deal, weighing 16.3 grs., similarly acted on, floated ten days;—and a portion of the pith of the elder, weighing only .133 grain, floated seven days.

The pleasure which honourable and enlightened minds must feel in acknowledging their obligation to the individuals who have advanced useful knowledge in any department of science,—who have contributed to the means of promoting human happiness, or of alleviating human suffering, has, in all times, led men to seek an opportunity of recording their sentiments of admiration and of gratitude towards the distinguished instructors of mankind. They have felt, too, that the time when one of these guiding lights has been quenched, when a contributor to the treasury of knowledge has just terminated his labours, is peculiarly fitted for the discharge of this duty. The whole amount of his contributions is then presumed to be before them, and they are restrained by no fear of offending his delicacy by their praise, or of having their own feelings hurt by a misconstruction of their motives.

It was observed by Fahrenheit, that the boiling point of water depends on the height of the barometer, the pressure of the air hindering the conversion of water into steam by a resistance which must be overcome by an increase of heat. Deluc and De Saussure contrived apparatuses for making the observation in the open air, and at great heights, and appear to have contemplated the substitution of the thermometer for the barometer upon occasion. They, as well as Dr Horsley, Sir George Schuckburgh, and Mr Cavendish, seem to have regarded the question as one which concerned the fixity of the point used in graduating thermometers, and its requisite corrections, rather than as applicable to barometric purposes generally.

Ever since the discovery by Berzelius of crenic acid in the iron ochre of the water of Porla, in Sweden, chemists have admitted the usual presence of that acid in mineral waters, or those springs containing notable quantities of dissolved inorganic constituents. In such natural waters, also, as are visibly coloured, organic matter is usually understood to be present. Any ideas, however, which may have been entertained respecting the occurrence of organic matter in the perfectly colourless, transparent, and comparatively pure water of ordinary springs, wells, and rivers, have been merely vague and conjectural.

About three years ago, I received from my friend Dr Watt of West Coast, Demerara, specimens of the bark of a tree, native of British Guiana, which had been found by Mr Rodie, late surgeon R.N., to contain a vegetable alkali, and to possess some value as a remedy in the intermittent fevers of that colony. Mr Rodie made known his discovery by means of a letter which he published in the year 1834. I made some experiments with the piece of bark, at that time in my possession; but the conclusions at which I then arrived did not appear to be worthy of being published. It was obvious to me, however, from the results which I obtained, that Mr Rodie's statement was so far correct, that the bark did contain a bitter matter, having all the general characters of a vegetable alkali, and capable of forming neutral compounds with acids. The exhaustion of my original little store of materials prevented me from proceeding farther, till last year, when,through the kindness of Dr Watt, I received a barrel of the bark, and likewise of the fruit of the plant.

It seems extraordinary, that no one should have undertaken a geological survey of Roxburghshire, more especially as the counties to the east and west of it have been examined, and accounts of their formations were published some years ago. It cannot be from its uninteresting character, that the intervening district has been neglected; for it presents as great a variety of apparently distinct formations, as there are in the adjoining counties of Dumfries and Berwick; and some of these have long been the special subjects of speculation and controversy among geologists. The British Association, in the Report of its Meeting held at Cambridge in 1833, propounded the following questions for geological inquiry.