the free passage of all the others. The following figures will assist my

explanation:

Fig. 1. Represents the prismatic spectrum as formed by a pure flint glass prism.

Fig. 2. Shows the same spectrum after it has passed the glass selected for the Palm House. It will be seen that the only difference which this produces upon the rays of Light, is that it cuts off a small portion of the lowest red ray, and slightly diminishes the length of the yellow ray by increasing the green. By this it will be seen, that no ray is lost, and consequently no difference can be perceptible in coloured bodies viewed under this glass; the Light which passess it is still pure white Light, and we have no chromatic disturbance; a red flower, although the red ray is the most influenced, still finding enough of red Light to maintain its natural colour.

Sir William Herschel and Sir Henry Englefield proved the existence of the largest amount of heat in the lowest red rays, and over a space below them where no luminous rays could be discovered. Sir John Herschel confirms this, and he has proved it in a very ingenious manner. Silver paper stretched upon a frame is smoked over on one side, and being washed with ether is exposed to the action of the spectrum; under these conditions the paper dries over spaces such as are represented in Fig. 3. The maximum point of heat is shown by the rapid drying of the spot a, long before any action is exhibited on any other part, but eventually the other spots and spaces make their appearance on the marking out the limits of the solar heat radiations.

paper,

By exposing leaves, and the green colouring matters of leaves, to the action of the prismatic spectrum, I find that they are rendered brown by exactly this class of rays-the browning in no instance going on beyond the orange rays, and only very slowly and faintly over the space covered by the visible red rays, many hours being required to produce any change under the influence of orange-coloured Light.

Fig. 4. Shows the effect of interposing the selected glass. All those heat rays which produce the scorching of the leaves are cut off, and thus the plant, by its use, would be protected from the injury complained of.

That this is the case I have proved by procuring the colouring matter from the palm leaves themselves, with which I was furnished from the Royal Botanic Gardens at Kew, by Sir William Hooker.

Several vessels filled with solutions of this colouring matter being exposed under various conditions to the influence of sunshine, it was found that those solutions which were protected by the green glass retained their colours unchanged, whilst the others exposed to the direct action of Light, or behind white glass, entirely lost colour.

The Commissioners of Woods.

ROBERT HUNT.

11th January, 1847.

MY LORD AND GENTLEMEN,-As it has been thought desirable to place the Board in possession of the principles upon which the green glass selected by me, and approved by Sir William Hooker and Mr. Decimus Burton, has been chosen, I have the honour to submit the accompanying memorandum as an addendum to my former report. I have the honour to be, &c.

The Commissioners of Woods.

ROBERT HUNT.

No. V.

ON THE "CHEMICAL RAYS," BY M. E. BECQUEREL.

[Referred to from pages 351. and sequel.]

THE following extract from the memoir previously referred to will show the discrepancies in the results obtained by Becquérel in Paris, and those procured in England. Reference to the frontispiece will render the descriptions of M. E. Becquérel sufficiently clear :

"Si l'on étend du chlorure d'argent sur du papier blanc, ou sur une surface quelconque, et qu'on l'expose dans le spectre, on voit, au bout d'un temps plus ou moins long, une réaction commencer vers l'extrême violet, entre les raies H et G de Fraunhoffer, et s'étendre d'un côté dans le spectre presque jusqu' en F dans le bleu, et de l'autre bien au delà du violet visible; mais si le chlorure d'argent, après avoir été préparé dans une chambre parfaitement obscure, est exposé pendant un temps trèscourt à la lumière diffuse ou solaire, mais de manière à ce qu'il ne soit pas noirci, mais qu'un três-faible commencement d'action ait en lieu, si on le place après dans le spectre, on voit non-seulement une colouration vers le violet extrême, mais encore une action se manifester en même temps dans la partie la moins réfrangible du spectre jusqu' au rouge extrême, de sorte que l'espace noirci se trouve dans toute l'étendue du spectre lumineux, et bien au delà du violet. D'après le mode d'action de la lumière, j'avais nommé les premiers rayons situés vers le violet rayons excitateurs, et les autres rayons continuateurs, parce qu'ils continuent une action chimique commencée sous l'influence des premiers.

Ainsi, lorsque le chlorure a été primitivement un peu impressioné, l'étendue de la partie colorée se trouve depuis le rouge extrême, jusque bien au delà du violet, mais il y a deux maxima d'intensité d'action, l'un entre Get H, l'autre entre D et E, vers le jaune, et correspondant aux rayons continuateurs.-Si l'on emploie du bromure d'argent préparé par double précipitation au bien par double décomposition sur du papier en

étendant un bromure soluble, puis du nitrate d'argent on obtient les mêmes effets, se ce n'est que l'action s'étende plus ou moins loin au delà du violet, et que les maxima ne sont peutêtre pas aux mêmes places; mais si'l y a une différence, elle est très-faible. L'iodure d'argent, et en général presque tous les sels d'argent, éprouvent la même action de la part des rayons solaires; les plaques d'argent iodurées à la manière de M. Daguerre, et même rendues plus sensibles à l'aide du chlore et du brome, éprouvent les mêmes réactions, si ce n'est que les rayons excitateurs s'étendent un peu plus ou un peu moins loin; et même on a remarqué que les maxima changent un peu de place, de sorte qu'en employant telle on telle préparation d'argent, la position du maximum des rayons excitateurs n'est pas la même; mais ils sont généralement situés, entre H et G, et entre D et E. *** Si, au lieu de placer dans le spectre des papiers ou des surfaces enduites de matières impressionnables formées avec des sels d'argent, ou place un papier préparé avec du bichromate de potasse, alors, au bout de quelque temps, on voit une réaction commencer vers F à la limite du vert et du bleu, puis s'étendre d'un côté en E, et de l'autre au delà de H vers M, de sorte que le maximum a lieu vers E.

Si l'on emploie un papier enduit de résine de gaïac, on le voit bleuir au delà de H, le maximum étant vers M; si au contraire, on place dans le spectre du gaïac bleui à la lumière, alors le gaïac redevient blanc dans le spectre, depuis le rouge A jusqu'en H le maximum étant vers F.(Annales de Chimie et de Physique, November 1843.)

No. VI.

ON THE DISCOLORATION OF PHOTOGRAPHIC PAPERS BY ELECTRICITY, AND THE PRODUCTION OF ELECTROGRAPHS.

[Referred to from page 265.]

M. AUG. PINAUD has studied the action of static-electricity on the chloride, iodide, and bromide of silver, comparing it with the action of Light on the same bodies. A notice of these researches has appeared in the "Comptes Rendus." He has found that electricity proceeding from a point, whether positive or negative, imparted brilliant spots of a bluish colour to the ioduret of silver on a prepared Daguerréotype plate, and by this means all sorts of figures can be traced upon it. M. Matteucci has shown that an instantaneous escape of electricity, without visibly affecting a silver plate, occasions on its surface a deep and lasting alteration, which is rendered evident by the condensation of the breath or any vapour on the plate. The vapour condenses around the part which has received the electricity, and tarnishes the metallic surface, but the points, which have been acted on by the electric fluid, remain bright. This fact serves to confirm the position I have maintained in opposition to Möser, that the condensation of vapours may be effected by other influences than Light. M. Pinaud exposed paper pasted on an insulated metallic plate and covered with dry bromide of silver to the action of electricity from a very

C C

fine metallic point electrized negatively by induction. Opposite the point a spot of a blackish brown colour is immediately formed. By passing the point over the paper any figure can be sketched out. The discoloration thus obtained has a deep brown shade like that produced by Light. If the metallic point touches the paper, the discoloration is then a deep black, and limited to the points which are touched; and the effect is that of a black-lead pencil. Positive electricity does not appear to produce any effect upon the bromide of silver. On the nitrate of silver and the chloride the electric fluid effects but little change; iodide of silver on the contrary is, when spread over paper, readily changed by either positive or negative sparks; the negative spark forming a round black spot, the positive developing in all the filaments of the paper, amongst which it is diffused, a violet discoloration in a radiated form. If paper covered with the iodide of silver is placed upon the insulated stand of a universal discharger, and the spark of a highly-charged jar is passed from point to point along a distance of an inch or two, the trace of the spark is instantly impressed upon the paper by a reddish train, which records all its windings and sinuosities.

Another method adopted by M. Pinaud for obtaining electric pictures is, to place a sheet of dry iodized paper upon a spotted glass plate, and retain it by means of a glass plate slightly pressed against it. The discharge of a powerful Leyden jar is then passed along the metallic ribbon, and each space is marked by a spark, and spots are formed on the paper at all the corresponding points. The analogy between these phenomena and those produced by solar agency are striking, and they well deserve investigation.

No. VII.

THE NON-EXISTENCE OF ANIMAL AND VEGETABLE LIFE IN THE DEPTHS OF THE OCEAN.

[Referred to from page 353.]

PROFESSOR FORBES, of King's College, London, who was engaged during eighteen months on researches in the Egean Sea and on the coasts of Asia Minor, during which time particular explorations of the sea bottom were made by means of the dredge, has defined the depths at which various species of animals and vegetables exist. He has proved by the decisive evidence of actual examination that, below the depth of thirtyfive fathoms, the number of animals diminishes as we descend, until at the depth of about 200 fathoms the number of testacea was found to be only 8, and a zero in the distribution of animal life was indicated at probably about 300 fathoms. Green fuci were not found below 55 fathoms, and millepora not deeper than 105 fathoms. I am informed by my friend, Mr. Richard Couch of Polperro, who has exhibited the most indefatigable spirit in his researches around the south coast of Cornwall, that he has found the same law to be maintained over this portion of the British Channel. Vegetable and animal life ceases at about the same

depths as in the Egean Sea. We may therefore infer that this condition is maintained, or nearly so, over every part of the ocean. Professor Forbes and Mr. Couch have, both of them, remarked that the vegetables and animals near the surface of the sea are brilliantly coloured, but that they gradually lose the brightness of their hues as they descend, until the animals of the lowest zone are found to be nearly colourless. Hence we see the dependence of marine, animal, and vegetable life upon the solar influences, to as great an extent as over the surface of the dry land. M. E. Becquérel's position is not a good one, and it affords us no evidence that any marine animal has the powers of vision under the influence of such rays of Light as would not excite the optic nerve of man. Organisation and life exist only at the surface of our planet, and under the influence of Light. Those depths of the ocean at which an everlasting darkness prevails is the region of silence and eternal death.