At the time of the fire the heat was so intense, that the iron safes, with gold and silver in them, melted, and became consolidated masses. The work of plunder commenced by some of the negroes, when it was found expedient to call out the military, and report says many of the negroes were shot in endeavouring to resist the military. Several French ships of war repaired to the spot, and on Sunday, the 12th inst., were to bombard the remaining standing walls. How the fire originated has not been ascertained. Some suppose it was from the earth, others that it was from the stores. Loss of life cannot yet be ascertained; variously reported at 4,000 to 5,000 and some say 6,000 souls. Basse Terre has not sustained any injury. DOMINICA.-Violently shaken; no real mischief done. Refugees arriving from Guadaloupe. MARTINIQUE.-Shaken, but no injury in town sugar mills a little damaged. ST. LUCIA.-A little shaken, but no injury. At the time of the earthquake the ship was off the island of Porto Rico; no shock was felt on board. (Signed) Your most obedient humble servant, WM. HELMSLEY, Captain. To His Excellency the Right Hon. Sir Charles E. Grey, &c. By SIR On the Action of the Rays of the Solar Spectrum on Vegetable 149+ IN my paper on the "Chemical Action of the Solar Spectrum on preparations of Silver and other substances," read to the Royal Society in February, 1840, andof which the present communication is intended as a continuation or supplement, some experiments on the effect of the spectrum on the colouring matter of the Viola tricolor, and on the resin of guaiacum are described, which the extreme deficiency of sunshine during the summer and autumn of the year 1839 prevented me from prosecuting efficiently up to the date of that communication. The ensuing year 1840 was quite as remarkable for an excess of sunshine as its predecessor for the reverse. Unfortunately the derangements consequent on a change of residence prevented my availing myself of that most favourable conjuncture, and it was not till the autumn of that year that the inquiry could be resumed. From that time to the present date it has been prosecuted at intervals as the weather would allow, though owing to the almost unprecedented continuance of bad weather during the whole of the past summer and autumn (1841), it has of late been almost wholly suspended. In photographic processes, where silver and other metals are used, the effect of light is so rapid that the state of the weather, as to gloom or sunshine, is of little moment. It is • From the "Phil. Trans. for 1842." Read, June 16th, 1842. The parapraphs, for convenience of reference, are numbered in continuation of those of the previous paper referred to in the text. otherwise in the class of photographic actions now to be considered, in which exposure to the concentrated spectrum for many hours, to clear sunshine for several days, or to dispersed light for whole months, is requisite to bring on many of the effects described, and those some of the most curious. Moreover, in such experiments, when unduly prolonged by bad weather, the effects due to the action of light become mixed and confounded with those of spontaneous changes in the organic substances employed, arising from the influence of air, and especially of moisture, &c., and so give rise to contradictory conclusions, or at all events preclude different results, and obscure the perception of characters which might serve as guides in an intricate inquiry, and afford hints for the conduct of future experiment. It is owing to these causes that I am unable to present the results at which I have arrived, in any sort of regular or systematic connexion; nor should I have ventured to present them at all to the Royal Society, but in the hope that, desultory as they are, there may yet be found in them matter of sufficient interest to render their longer suppression unadvisable, and to induce others more favourably situated as to climate, to prosecute the subject. 150. The materials operated on in these experiments have been for the most part the juices of the flowers or leaves of plants, expressed, either simply, or with addition of alcohol, or under the influence of other chemical reagents. Some few resinous and dyeing substances have also been subjected to experiment, but with less persevearance than the obvious practical importance of this branch of the subject might demand, except in the case of guaiacum, whose relations to light, heat, and chemical agents are exceedingly remarkable and instructive, for which reason, as well as because some of these relations have been treated of in my former paper, I shall commence the account of my latter experiments with those made on this substance. But in the first place it is necessary to state that the apparatus used for forming, concentrating, and fixing the spectrum, was the same with that described in Art. 67. of that paper; the prism being that of flint-glass by Fraunhofer, there mentioned; the area of the section of the incident sunbeam 154 square inch, and the dimensions of the principal elements of the luminous spectrum, identical with those recorded in §. 70, so that the following results, when numerically stated (in measures of which the unit is one-thirtieth of an inch), will be comparable with those previously described. To spare reference, however, it may be here mentioned that the diameter of the sun's image in the focus of the achromatic lens used is 7.20 of such thirtieths; and that the extent of the visible spectrum corrected for the sun's semidiameter at either end, equals, 53-92 thirtieths, of which 13:30 are considered as reckoned negatively to the extreme visible red from a fiducial point or centre corresponding to the mean yellow ray; and 40.62 positively, from the same centre to the terminal violet, both as seen through a certain standard blue glass, which lets both extremes pass freely and insulates the mean yellow with considerable precision. The correction for the sun's semidiameter has been applied in what follows to all measures up to terminations of spectra, unless where the contrary is expressed. Maxima and minima of action, and neutral points neither require nor admit this correction. Guaiacum. 151. A solution of this resin in alcohol, spread evenly on paper gives a nearly colourless ground. A slip of this paper exposed to the spectrum is speedily impressed with a fine blue streak over the region of the violet rays, and far beyond, as described in Art. 92. If the paper during this action be carefully defended from extraneous light, this is the only perceptible effect; but if dispersed light be admitted, the general ground of the paper is turned to a pale brownish green, with exception of that portion on which the less refrangible rays fall, which, by their agency, is defended from the action of the dispersed light, and preserves its whiteness, as in the case of the argentine paper described in Art. 60. The spectrum, therefore, ultimately impressed, consists of two portions similar to those described in Art. 93, and of nearly the same extent, that is to say, a white or pale yellowish portion having its maximum of intensity at 0-0, and extending from -11.9 (corrected for the sun's semidiameter) to +120, or thereabouts, at which point the character of the action changes, and a blue, of a somewhat smoky gray cast, commences, which attains a maximum at +400, thence degrades to an intermediate minimum at +470, attains a second and much stronger maximum at +610, and ceases at 72.4. The precise numbers vary materially in different specimens and with the length of exposure. The type of this spectrum, of its natural length, is represented in Plate 3. fig. 1, in which the abscissæ being measured along the length of the spectrum, from the fiducial centre Y both ways, the ordinates express the intensities of photographic action at each corresponding point, as estimated from the amount of colour induced or prevented. In this type the portion corresponding to the less refrangible rays is represented by negative values of the ordinate agreeably to Art. 93, where it is shown that these rays not only prevent the blue colour from being produced by the more refrangible ones, but destroy it when so produced. Another specimen gave the following dimensions: Y a = -11·4, Y b ——9·5, Y c = + 30·0, Yd=610, Ye+ 80·4, and this is the greatest extent of action I have hitherto observed. 152. A portion of the same paper was exposed, dry, to an atmosphere of chlorine considerably diluted with common air, which imparted to it a pale, dirty, greenish yellow hue. Being thence transferred immediately to the spectrum, the result was not a little remarkable, the whole spectrum, the green excepted, was impressed in faint tints nearly corresponding to the natural ones. The red was evident-the yellow dilute and nearly white-the blue a fine sky-blue, while beyond the violet succeeded a train of somewhat greenish darkness. These tints proved fugitive, and in twenty-four hours were nearly obliterated. 153. When paper fresh washed with tincture of guaiacum and still wet is exposed to chlorine, it instantly acquires a fine and full Prussian blue colour, which however passes speedily to brown if the action be prolonged. The colour is difficult to preserve in its full intensity, and fades considerably in drying, becoming at the same time somewhat greenish. Exposed wet to the spectrum, it is found to have become much more sensitive, and is immediately attacked with great energy by the red rays, which destroy the blue colour, converting it to a brownish or reddish yellow. The action extends rapidly up the spectrum as far as the extreme violet, in which ray, however, the tint impressed or left undestroyed passes to a hue partaking of violet, and indicating by the changes what ought probably to be regarded as a neutral point at +120. The impressed spectrum (corrected for semidiameter) commences at a, fig. 2, at— 13·4; the maximum b of the positive action occurs at 90, the neutral point c at +12.0, the maximum d of negative action at + 33 0, and the sensible termination e of the impression at + 60.0. 154. The action of gaseous chlorine is too energetic to be easily arrested at the proper point, besides which this gas also acts powerfully on the alcohol employed. To obviate these inconveniences, paper thoroughly impregnated with guaiacum by washing with the tincture, and drying in a gentle heat, was steeped in weak aqueous solution of chlorine, by which process it slowly acquired a beautiful and pure celestial blue colour. It is very sensitive and may be conveniently used for copying engravings, &c., which it does with this singularity, that the picture penetrates the paper, and appears on the back of very nearly the same intensity as on the face. Indeed, if the picture be over-sunned the back will exhibit a perfect impression, while the face is spoiled, which produces a very strange effect: exposed to the spectrum, the blue colour is converted to a pale reddish yellow in the region of the less refrangible rays, and simply whitened in the more refrangible region. The action, when prolonged till the light seems to have no further influence, extends from -124, corrected for semidiameter, to +40, or thereabouts, where it dies away insensibly. The maximum of photographic action occurs at -87, and some trace of a minimum is perceptible at +115. Photographs taken on this paper, or spectra impressed on it, are fugitive-lose much of their force and beauty in a few days, and at length vanish altogether. 155. When paper is washed with a solution of guaiacum in soda, it acquires a green colour, though the solution itself is brown. By inclining the paper and carrying the wash always from below upwards, a very even tint may be obtained. The excess of liquid being blotted off, aqueous solution of chlorine was poured over it, (on a slope) till all the alkali was saturated, and the liquid ran off smelling strongly of chlorine. Thus was produced a paper (No. 1168) very evenly tinted, and varying in colour from a deep, • For another remarkable case of this kind, see the Postscript to this paper. somewhat greenish, to a fine celestial blue, according to the strength of the solutions employed. It is very sensitive, and is attacked with especial energy by rays in the spectrum, ranging from -114 to 114 with a maximum at -90, the type being as in fig. 3. 156. When paper so prepared is exposed, wet, to a temperature of 212 Fahr., it is immediately discoloured, the green changing to a sere or brownish yellow. The same change is produced, after some little time, at a temperature of 190°, and still more slowly, though yet completely, at 180°. At 175° the discoloration is incomplete and very slow; and below that temperature the colour is not affected. If the paper be perfectly dried in a temperature gradually raised to 212°, the discoloration requires a considerably higher temperature, ranging from 220° to 275°, according to the time of exposure, being very slow at the former limit, and almost immediate at the latter. These changes are independent of the action of light, being produced under mercury. 157. The destruction by heat of the green or blue colour, superinduced on guaiacum by the more refrangible rays of light, was noticed by Wollaston, and it would seem, on a consideration of his experiments, and of those described in the last article, that nothing further is requisite for operating the change from the green or blue to the yellow state, than the assumption of a certain temperature dependent on its state of dryness, and varying according to that state between the limits of 180° and 280°. Nevertheless, if we consider that the same change is produced by rays of the spectrum which are very far from being the hottest, while yet the extraspectral thermic rays, under precisely the same circumstances of exposure, produce no such effect, though far surpassing in mere calorific power those which do, we shall see reason to doubt the sufficiency of this view of the matter. The following experiments were therefore instituted, with a view to its further elucidation. 158. A slip of the paper No. 1168 was moistened, and subjected in clear sunshine to the action of the spectrum. The colour was discharged from the region occupied by the less refrangible luminous. rays, as described in Art. 155. At the same time, the more distant thermic rays beyond the spectrum produced their proper effect, in evaporating the moisture from those portions on which they fell; so that in due time the heat-spots and y became apparent (see Art. 136), the former very distinctly, the latter perceptibly. The spot ẞ (which is remarkable) was scarcely if at all formed. So long then, as the paper continued moist, and remained under the influence of the thermic rays, the appearances were those of a diminution of colour (Art. 131), operated by the thermic rays & and y. But the discoloration in these points was only apparent, for as the paper dried these heat-spots disappeared, leaving its colour quite unchanged at those points; while the photographic impression really produced within the visible spectrum, remained and went on increasing in intensity. The non-luminous thermic rays, therefore, though clearly shown to have been active as heat, were yet incapable δ |