It is asserted by Sir David Brewster, that "coal does not transmit to the eye a single ray out of those which enter its substance." Now, if when an opaque body discharges no light whatever from its internal parts, we have the phenomenon of blackness, even though the quantity of light reflected from its external surface is considerable, it must I think be admitted, that when such a body possesses a proper colour, its colour is owing to the radiation of coloured light from its pores.

In making a brief recapitulation of the views unfolded in this paper, I would say that the particles of all opaque bodies exercise over the intromitted rays a specific attractive power. Those of coal and other black bodies attract and detain the white light, but, having a feeble affinity for the caloric, the latter exists within such bodies in a free state, and then escapes from their pores by radiation and otherwise; the particles of white bodies detain the caloric, but, having less affinity for the white light, a large proportion of the latter exists within these bodies in a free state, and then escapes from their pores by radiation; and the particles of a body whose colour is one of the primary colours of the spectrum, attract and detain the light which is complementary to that which gives the body its proper colour, the latter, being left free, escapes from the internal parts of the body, by that self-repellent power of its particles which is known to exist, and is the cause of radiation.

This theory is one of extreme simplicity; but it is not for that reason the less likely to be true. We are taught by Sir Isaac Newton, that "Nature does nothing in vain, but is simple, and delights not in superfluous causes of things."-From Silliman's Amer. Jour.

ON THE GALLO-NITRATE OF SILVER OF MR. FOX TALBOT, AND ITS ACTION UPON IODIZED PAPER.

BY GEORGE S. CUNDELL.

SOME of the properties of this remarkable compound have been described by its inventor, and are sufficiently well known; the relations however of its constituent parts, and the means by which the action of the compound

may be regulated (some knowledge of which is indispensable to the using it with success), are less generally understood, and have not, so far as I am aware, yet been described.

When solution of the nitrate of silver is applied to iodized paper, a surface is obtained which is extremely sensible to the impressions of light: and, if gallic acid have been added to the solution, the sensibility of the surface will be increased in a remarkable manner.

Preparations however of this kind are subject to a spontaneous and rapid change, independently of light; and, where such have been employed, after a certain time (longer or shorter, according to the strength of the solutions), on developing an impression in the usual manner, it will be found that the whole of the surface, whether acted upon by light or not, will become dark and discoloured; and such preparations seem therefore to be of little or no value in photography.

By adding to them, however, a little acetic acid, the tendency to spontaneous decomposition is immediately lessened; and by combining the three constituents in due proportion, a "gallo-nitrate" may be formed of any degree of stability (or, inversely, of any degree of sensibility) required.

There are, no doubt, many proportions in which the ingredients may be united with good effect; but, for general use, no proportions perhaps are better than the original ones given by the inventor. It is to be observed, however, of his formula, that it is adapted to certain external conditions, and is not equally suitable where these are different. It is not equally suited to every climate or temperature of the air; and although well adapted to excite paper for immediate use, it is perhaps less so when the paper is intended to be kept: hence the cause of many miscarriages in its use, and the necessity for something more than a mere formula for its preparation.

If the acetic acid be deficient (which is frequently the case from its uncertain strength,) the spontaneous decomposition already noticed will take place with more or less rapidity; and, unless the paper be used without delay, the impression will be lost in the general darkening of the surface.

On the other hand, if the acetic acid be in excess, there will be less tendency to decomposition; the paper will

also be less sensitive, but it will much better preserve its whiteness in the excited state, and may be used successfully after many hours.

By thus tempering the compound with acetic acid, according to circumstances, it will be found that its action may in a great degree be brought under control.

If the gallo-nitrate of silver of Mr. Talbot be applied to iodized paper, an action commences, which, unless very quickly arrested, instead of merely exciting the surface and preparing it to receive an impression, will speedily darken and render it useless. It is most probably on that account that the paper is directed to be "dipped into water;" the effect of which is to arrest the action by diluting the gallo-nitrate, and by removing, perhaps, ninetenths of it from the paper. The extent, however, to which the destructive action may have gone, and to which the gallo-nitrate may thus have been diluted or removed, is all to the last degree uncertain; and it seems a more satisfactory proceeding to apply the gallo-nitrate in the diluted state, and to dispense with the dipping in water altogether.

The diluting is a very much simpler and more œconomical method, and it is evidently a more certain one.

If the gallo-nitrate be diluted not more than ten times, it imparts a high degree of sensibility, but in that case the paper must be used immediately. It may be diluted as much as forty times, and in favourable circumstances will still give an intense picture. In diluting to that extent the paper becomes less sensitive, but it is less subject to the spontaneous change, and preserves its useful properties much longer.

To develop an impression, the gallo-nitrate ought to be of the full strength, particularly in gallic acid, upon which the depth and intensity of the picture chiefly depend, and which in a saturated solution will be present in greater or less quantity, according to the temperature of the air, by which the general chemical action is also affected. From the Philosophical Magazine.

LIST OF IRISH PATENTS.

From July 14, to Sept. 19, 1846.

CHARLES HANCOCK, of Grosvenor-place, in the County of Middlesex, Gentleman, for Certain improvements in the manufacture of gutta percha, and its applications alone and in combination with other substances.-Sealed July 14, 1846.

GEORGE LOWE, formerly of Brick-lane, Old-street, in the County of Middlesex, but now of Finsbury Circus, in the said County, Civil Engineer, (extension of original patent,) for An invention for increasing the illuminating power of such coal gas as is usually produced in gas works; also for converting the refuse products from the manufacture of coal gas into an article of commerce not heretofore produced therefrom; and also of a new mode of conducting the process of condensation in the manufacture of gas for illumination.-Sealed July 14, 1846.

JOHN BROCKLEHURST, of Holborn, in the County of Middlesex, Lamp Manufacturer, for Certain improvements in the hanging and disconnecting of window sashes and frames.-Sealed August 11, 1846.

ROBERT HAZARD, of Clifton, near Bristol, in the County of Somerset, Confectioner, for Improvements in apparatus for heating public and private buildings.-Sealed August 24, 1846.

RICHARD WHYTOCK, of Edinburgh, Manufacturer, extension for five years, from August 15, 1846, of a former Patent, for An improved method or manufacture, which facilitates the production of regular figures or patterns on different fabrics, particularly velvets, velvet pile, and Brussels, Wilton, and Turkey carpets.-Sealed August 24, 1846.

GEORGE HINTON BOVILL, of Millwall, in the County of Middlesex, Engineer, for Improvements in manufac

turing wheat and other grain into meal and flour.-Sealed August 24, 1846.

WILLIAM GARNETT TAYLOR, of Halliwell, in the County of Lancaster, Cotton Spinner, and WILLIAM TAYLOR, of Halliwell, aforesaid, Labourer, for Improvements in consuming smoke, and economizing fuel.-Sealed August 31, 1846.

JOHN PATERSON REID, of the City of Glasgow, Gentleman, and THOMAS JOHNSON, of the same city, Mechanic, for Certain improvements in machinery for weaving, and for producing patterns in weaving, as also in machinery for finishing certain woven fabrics.-Sealed September 11, 1846.

JOHN ROBERT JOHNSON, of Alfred-place, Blackfriars, in the County of Surrey, Chemist, for Improvements in the materials employed in constructing and working atmospheric railways.-Sealed September 16, 1846.

JOHN SIMSON, of Riches-court, Lime-street, London, Merchant, for Certain improvements in machinery for preparing and spinning flax, and other fibrous materials. -Sealed September 19, 1846.—(Communication.)

LIST OF ENGLISH PATENTS.

From August 26, to September 25, 1846.

HENRY BESSEMER, of Baxter-house, Old St. Pancras Road, Engineer, for Improvements in railway engines and carriages, parts of which improvements are applicable to the propelling of steam vessels, and to motive purposes generally.-Sealed August 26, 1846.-(Six months.)

ALFRED KRUPP, Principal of the House of Frederick Krupp, of Essen, Prussia, but now of Leicester-square, Middlesex, for Certain improvements in the manufacture of spoons, forks, and other similar wares, and in the machinery or apparatus employed therein, parts of which