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here briefly to trace their progress to the On the as yet untouched iodated plate, present date.

the violet and blue rays are those alone It has for some time been known that of the spectrum which are active. They when an ordinary silver plate (prepared produce that invisible change of molefor Daguerreotype purposes) is exposed cular arrangement which is made visible for a certain time to light reflected from to the eye by the mercurial vapour ; but objects in the camera obscura, after there are two periods distinguishable in having received the coating of iodine va this action. At the end of the first, the pour, an image is produced of the objects red and orange rays act upon the plate on the plate, without the use of mercu as well as the blue or violet, and the yel. rial vapour. But the image is a negative low are inactive; at the end of the one ; that is to say, the lights and sha second period, the yellow and green rays dows are reversed. On the Continent, act in their turn. The plate is then just such an image is called negative, while at the point when the mercurial vapours an image in which the lights are light, act upon it in rendering the image visiand the shadows dark, is said to be po ble. sitive. In Daguerre's process, nothing When an iodated plate was exposed in appears upon the iodated plate until after the camera, until a very distinct negative it has received the mercurial vapour. image was produced of objects illuminated Nevertheless, the experiments of Edmund by sunshine, and the plate then taken Becquerel show that an extremely short out and exposed to direct sunlight, the time is sufficient to affect the iodated former image soon disappeared, and a surface in such a way that if the plate be positive image appeared in its place, in placed in the sunshine, under a red glass, which the lights had a green tint, and the latent image becomes gradually more the shadows a dark red brown. The and more visible or distinct, on applying latter effect Möser attributes to the yelthe mercurial vapour afterwards, al low and green rays.

When a plate though (it will be observed) the objects coated with chloride of iodine was exwhich originally, as it were, impressed posed in the camera, in winter, for thirthe image are no longer in presence. teen days, a positive image of great beauty Hence he has distinguished the acting was produced ; the lights had a sky blue rays into “exciting rays” and “continu colour, and the shadows a fiery red The ing rays."

plate being then immersed in a solution Möser has found that in the preceding of hyposulphite soda, the positive image case, if the action of the red glass be disappeared, and in its place came forth continued long enough, the image (a ne a negative one. gative one) appears without the use of Polarized and unpolarized light promercury at all.

duce precisely similar effects in these Gaudin had previously found that yel conditions. low glass acted as efficaciously, or more Placing a prism of carbonate of lime, red in these conditions.

achromatized, for one of the images before Möser has observed the following sin the lens of the camera, and adjusting for gular fact. A plate iodated, which had a statue as an object, two images were obbeen exposed in the camera for the usual tained upon the plate, of which one was time to give a positive image with mer achromatic to the eye. Images of colour. cury, was taken out, and placed in the ed rings, figures given by polarized light sun under yellow glass, no image being seen through crystalline plates, &c., as yet visible. Presently, a negative when received on the photographic plate

, image appeared, which disappeared again were identical with those seen directly in a few seconds: and in about ten or by the eye. fifteen minutes there appeared in its place It has been long known that when a a positive image.

plate of polished glass is written upon Here we may remark, that the rays with certain substances, the writing efpassing through the yellow glass played faced, and the surfaces cleaned, yet on the same part that the vapour of mer breathing upon the glass the characters cury does. The positive image will not reappear, by means of the different appear, using red glass, however long arrangement of the particles of moisture the exposure ; but it succeeds well with condensed from the breath. green glass.

Möser has extended this phenomenon

SO, thi

to all polished bodies, and to all sub also with a plate of glass, when breathed stances whatever used for writing on upon, or exposed to vapour of water. them; these being such, of course, as These experiments show that contact produce no visible change on the surface. of bodies produces certain effects analoIt is even true of an undisturbed surface gous to those of light; but a much more of quicksilver after many days, if not remarkable result of Möser's is, that any disturbed. If a perforated screen be two bodies, when sufficiently near, implaced against a plate of glass, and the press their image one on the other, allatter breathed upon, and the screen be Though both be in absolute darkness. now removed, and the glass again breath Thus an agate or an intaglio, placed ed upon, after the moisture from the first opposite to a polished silver plate, at a has evaporated, the form of the perfora small distance, in total darkness, after a tions will be rendered visible.

longer or shorter time, occasionally in Regnault thinks fatty matter deposited ten minutes, has impressed its image on from the breath may have something to the plate, visibly to the eye, without any do with this.

previous exposure to vapour. Möser has found that when solid ob Phosphorescence has nothing to do jects, such as medals, intaglios, &c., are with the phenomena ; and if they arise placed in contact with a silver iodated from radiation, it must be concluded plate, after a shorter or longer time an that the effect of the radiant matter image of every part of the surface in diminishes very rapidly with the amount contact is traceable upon the place. This of obliquity produced by the distance of takes place with equal rapidity, certainty, the object. and minute accuracy in total darkness An engraving, placed for about twenty as in daylight. An image of an object minutes upon a plate of polished silver, which has been in contact with a polish. leaves its image, rendered quite visible ed silver plate may also be obtained by by vapour of iodine and mercury aftermerely exposing it to the vapour of mer wards. cury afterwards, without any previous These remarkable results of Möser's application of iodine.

have been verified at Berlin by AscherFrom these facts he concludes that the sohn, and in presence of Encke. parts of a surface touched by another From these researches, of which the body, affect variable affinities for the foregoing is an imperfect outline, Möser vapour of substances to which it may be deduces the following general proposiexposed; so that contact here produces tions: an effect analogous to light. Thus when 1. Light acts on all bodies, and on all medals, rings, &c., were laid upon an in the same way.

Actions heretofore iodated place in total darkness for a known are particular cases of this general night, an accurate image of every line of proposition. the contact surface was formed when the 2. The action of light so modifies plate was exposed to vapour of mer the surfaces of bodies, that they concury. Plates treated in the same way, dense vapours differently after exposure but exposed to diffuse solar light, in place thereto, from what they do before. Daof the mercurial vapour, also showed the guerre's discovery is a particular case of images as before. The same plates, ex this proposition. posed to coloured rays, gave slight traces 3. Vapours are condensed more or only under red glass or yellow, but well less forcibly by bodies after being exdefined images under violet.

posed to light, in proportion to their When a polished plate of silver, which own tension, and to the intensity of the had never been before used, was exposed light. to sunlight for some days, under a black 4. Ioduret of silver, as is known, is at perforated screen, placed very close, but first blackened by light. not in contact with it, on exposure of 5. But if the action be continued, it the plate to the vapour of mercury, the becomes coloured. image of the perforations became dis 6. The different refrangible rays all tinctly visible. The same experiment act alike, but require different times to succeeds with a plate of copper, when produce like effects. exposed to vapour of iodine. The same 7. The violet and blue rays, and the

ver.

ness.

invisible rays of “Ritter,” rapidly ori 23. The latent light of chlorine, broginate the blackening of iodurate of sil. mine, chloride and bromide of iodine,

The other rays, to produce equal seem to be the same as of iodine simply. effects, require times inversely as their 24. As to the latent light of vapour of refrangibilities.

water, Möser can only say, that it is not 8. The colouration of 5 is produced red nor yellow, nor orange nor green. most rapidly by the red and yellow 25. Ioduret of silver owes its sensirays; the other rays require, to produce bility to light to the latent light of the equal effects, greater time, as their re

vapour of iodine. frangibilities are greater.

26. Ioduret of silver is not more sensi9. All bodies radiate light, even in ble to invisible rays than silver itself. total darkness.

Sone of these propositions admit of 10. A property which does not seem much doubt at present. Those, however, to be of the nature of phosphorescence; which merely enumerate facts in this for no difference of effect is perceivable general form are worthy of every atten. between the same body, after exposure

tion. to sunshine, and after being long in dark Since attention has been drawn to this

class of phenomena, other facts have 11. These rays act on all substances, been recorded, long since observed by like the direct rays of light.

other persons, but of a strictly analogous 12. These rays, insensible to the re and most interesting sort. Thus Breguet, tina, have a refrangibility greater than the celebrated chronometer maker, has those of direct or diffuse solar light. stated, in a letter to Arago, that he has

13. Two bodies in total darkness constantly observed the name of his firm, always mutually impress their images. which is engraved on the brass cap co

14. But, in consequence of the diver- vering the works of their watches, imgence of the rays, the bodies must be pressed, in an inverted image, on the very close (though not in contact), that polished interior of the watch case of the image may be visible.

gold or silver; the engraving having 15. Any vapour may be used to render been, of course, when the watch was shut such images visible.

up, for a longer or shorter time, in close 16. As these rays are more refrangible propinquity, but not in contact with, the than any hitherto known, they are those interior of the case, and in total darkwhich ordinarily commence action (as in 7) on other bodies.

Further, M. Rauch, the sculptor, bas 17. There exists a latent light, as there observed a complete image formed on is known to exist a latent heat.

the surface of a plate of glass, which had 18. When a liquid is evaporated, the covered an engraving, of the subject of Jight which corresponds to a certain pe the print, although the glass did not riod of time, becomes latent, and is again touch it; and, it seems, this fact is familiberated when the vapour is condensed.

liar to engravers. 19. Hence it is, that light and vapours Möser has found that these images of produce in some respects the same prints on glass may be produced in a effects.

very short time.

The image appears 20. The condensation of vapours on brighter or lighter coloured than the plates acts like light; so that vapour in rest of the glass, and is easily rubbed excess simply adheres—as the vapour off. of water to most substances-or acts An engraving takes nine days to propermanently in adhering, as vapour of duce such an image, at a distance of mercury; or, finally, acts chemically, from ito % of a line of the glass. as vapour of iodine.

He has produced similar images on 21. The latent light of the vapour of surfaces of copper, brass, zink, and gold, mercury is yellow; all the actions which in five days. Möser proposes to repeat the yellow ray produces can also be pro- his experiments in vacuo, and is at preduced by the vapour of mercury. sent eagerly occupied with them.

22. The latent light of vapour of Amongst other Continental discoveries iodine is blue or violet, and the actions relating to photography, is that of M. of these rays can be produced by its ya- Lechi, of a mode of colouring Daguerreopour.

ness,

types, after they have been formed by the pipes, or any more of your space with the usual process. The general outline the matter. of the process, of which no details have I remain, Sir, yours respectfully, yet been published, consists in covering

WM. BADDELEY. each portion of the plate with a coat of

29, Alfred-street, Islington, transparent colour, of the required local

November 19, 1842. tint, in water-colours, and washing off the excess of non-adherent colour almost instantly in warm water ; enough adheres

CANAL NAVIGATION. -it appears, in fact, to sink into the plate-to give all the effect, it is said, of

Sir,-Having recently visited a neigha very finely finished, but peculiar look

bourhood where a canal, depending upon ing water-colour drawing.

casual supplies, is often, if not always so The applications to forgery, it may be

low towards the end of summer as to aladded, which Möser's discovery will soon

low of no more than half cargoes being afford, will, before very long, render new brought up, and that, often, at the exand difficult means requisite to prevent

pense of six or eight horses to drag the it in the preparation of bank notes, bills,

barges by sheer force over the bottom, it &c.

was suggested to me by a gentleman, R. M.

that rollers might be advantageously applied, and upon consideration, I beg to

submit, through the medium of your CLEANSING OF WATER PIPES. valuable Magazine, the following plans Sir,-Some remarks have recently for the comments of those practically acbeen made in your Magazine on the quainted with the subject of canal naviaccumulation of dirt in the mains of the gation, of which I freely confess my own water companies, and the great difficulty ignorance. My object would not be maof cleansing them, which, it is supposed, terially to increase the cargo at such can only be done by “taking them up,' times, but merely to render a much and this is rightly judged to be too ex

smaller amount of power necessary to pensive a remedy to be even “ hoped drag the barges over the flats. I propose for."

to furnish each flat-bottomed barge with I think a very small share of common three or four, or any other number of castsense, rightly applied, will enable every iron rollers, say, 6 or 12 inches diameter, impartial reader to perceive that this running on pivots, 6 or 12 inches long, would not only be an expensive, but at certain distances along her bottom, on really a needless remedy.

each side about half way between the Either the objectionable deposits in keelson and the extremity of her bottom, the water pipes are capable of being such rollers to project only such a disacted upon and removed by the water, tance as may be deemed or found most or they are not. If they are capable of advantageous, and to run in recesses conbeing carried off by the current, it is

structed in the bottom for the purpose, only necessary to get that useful func. which could be easily contrived. tionary “the turncock” to open a plug or It may be objected, that the rollers two on the lower levels of the district, to would be useless in muddy bottoms, but get rid of the offending matters at once. I would submit, that as mud accumulates But, if there be any deposits that are generally in the holes, or deeper parts of of such a ponderable character as not to water, leaving the shallower parts free be moved by the rush of water towards from it, the cbjection, taken generally, these large orifices on a low level, we does not militate against my plan. It is may depend upon it, they will never not improbable that some such may alannoy us by ascending through the in. ready be in existence, of which myself strumentality of a more moderate stream and neighbours would feel obliged for into our elevated cisterns.

an account. The remedy referred to above, is the I remain, Sir, yours, respectfully, one that is almost daily employed in va

J. B. S. C. rious parts of the metropolis, and is so Oakham, November 19, 1842. efficient for the purpose, that there is really no necessity for taking up, either

FOUR-WHEEL LOCOMOTIVE ENGINES, AND THE EFFECT OF INSIDE AND

OUTSIDE BEARINGS. Sir,-Being constant readers of your you gave a garbled extract of M. SeMagazine, the letter of your correspond- guier's opinion, delivered to the Royal ent, signed “ A Practical Engineer,” in Academy of France.

We can only your October Number, page 341, in quote your own words, as applied by you respect to the jumping of four-wheeled to the second communication on that locomotive engines, did not escape us ; article, if M. Seguier has been rightly and we have been considering whether, reported, and say, " It affords an admiafter all the proofs which have been rable specimen of the talent in which afforded of the superiority of four-wheeled Frenchmen art so peculiarly happy, of engines (provided, always, that they have slurring over a difficulty, and raising a inside framings), it was worth our while fog about a subject, which, while they to take the trouble of replying to a per do not understand, they will not admit son who fights behind a mask, and their ignorance of." We fear many of attacks opposing opinions under an our soidisant practical engineers' are in anonymous signature. Our inclination the same predicament as the Frenchmen. was to let such a person sleep quietly in Trusting to your candour for the inthe obscurity he had chosen, as an object sertion of this letter, we are, Sir, unworthy our notice. But in your No Your obedient servants, vember Part, in which you have spon

BURY, Curtis, & KENNEDY. taneously inserted our circular, and

Clarence Foundry, Liverpool, a sketch of our four-wheeled engines,

December 8, 1842 you prefix some remarks of your own, P.S. We enclose a lithographed sketch in which you refer to the communication of the effects of inside and outside fram. of the “ Practical Engineer,” as coming ing, with the broken axle, which illusfrom a “gentleman of as high authority trates what you are pleased to call "the in railway matters' as ourselves. We, singularly ill contrived and inconclusive therefore, now call upon that gentleman experiment on the London and Birming, to come forth and state his name, that ham Railway," and which we think will the public, as well as ourselves, may convey some instruction of an useful and judge of his “authority" in such matters; interesting nature to your

readers. and that we may have the opportunity [We give on the opposite page the not only of meeting the statements he engravings referred to by Messrs. Bury, has ventured to put forth, but to enter Curtis, and Kennedy, and subjoin their the lists with him, in the open face of explanation of the figures.] day, upon the whole question --- for The effect of inside and outside bearwhich we are fully prepared. The pub ings practically explained. lic will then be able to judge for itself. Figs. 1 and 2. Locomotive engine with We cannot think this gentleman will inside framing. decline our challenge, and shrink from Figs. 3 and 4. Locomotive engine with avowing himself; or that you will refuse outside framing the insertion in your Magazine of a dis Figs. 1 and 3. Show the position of the cussion which you have assisted in pro wheels with the axle broken. voking by your own remarks. At the Figs. 2 and 4. Show the position of same time we reserve to ourselves the the wheels in both engines when running right to decline entering into the contro on the railway. versy, if your correspondent should per Explanation of Figs. 1 and 2.-In chance prove to be a person of whose this engine the bearings are inside the authority in such grave and important wheels, and the weight of the engine matters we have no opinion; and we and boiler is carried at A A. The tenshall not hesitate publicly to give that as dency of the axle, therefore, is to bend our reason in such a possible case. downwards in the centre, whilst the pres

We take leave to advert here briefly sure of the flange against the rails in to your article in the October Number, headed “ Progress of Foreign Science, • How "garbled !" Imperfect it may possibly on the subject of the Versailles railway

be; but garbling implies intentional misrepre

sentation, and every thing of the sort we most dia accident, of the 8th of May last, in which

tinctly disclain.-ED. M. M.

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