The usual methods of obtaining pure phosphoric acid by the oxidation, with nitric acid, or by combustion, of pure phosphorus, are well known; but, although they yield a pure product, yet, as the phosphorus must be prepared from phosphoric acid, it is obvious that we shall derive a great advantage from any method of purifying easily and cheaply the phosphoric acid from bones, instead of first reducing it to phosphorus, and then re-oxidizing it. In practice, phosphorus is made from the superphosphate of lime, and it is from the same salt that phosphoric acid may be most economically prepared.

The Balance Magnetometer was imagined by Dr H. Lloyd, of Dublin, for the purpose of observing the variations of the vertical component of the earth's magnetic intensity. It consists simply of a balanced magnetic needle, with a knife-edged axle, resting on agate planes, at right angles to the plane of the magnetic meridian. In the instrument from which the results in this paper are deduced, the position of the needle is observed by means of micrometer microscopes.

While examining, in polarised light, the form and structure of the numerous crystals which I had discovered in the fluid cavities of Topaz, my attention was particularly called to certain optical phenomena exhibited in other parts of the specimen. These phenomena, when first presented to me, were very indefinite in their character, and very imperfectly developed; but after a diligent examination of nearly 900 specimens of topaz, I succeeded in obtaining the most satisfactory exhibition of them under various forms, and in various degrees of intensity.

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.

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.

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.