102 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



twelve months from tlieir foiniation, have, nevertheless, somewhat altered 

 durint; the second year. This circumstance, added to the fact that the first 

 attempts which I made became indistinct in process of time (the paper 

 growing wholly dark), induced me to watch the progress of the change 

 during some considerable time, as I thought that perhaps all these images 

 would ii/limalfli/ be found to fade away. I found, however, to my satisfac- 

 tion, that this was not the case ; and, having now kept a number of these 

 drawings during nearly five years without their sutfering any deterioration, I 

 tliink myself authorised to draw conclusions from my experiments with more 

 certainty. 



2. ICJIect and Appearance of these Images. — The images obtained in this 

 manner are themselves white, but the ground upon wliich they display them- 

 selves is variously and pleasingly coloured. 



Such is the variety of which the process is capable, that by merely vary- 

 ing the proportions, and some tritling details of manipulation, any of the 

 following colours are readily attainable : — Sky blue, yellow, rose-colour, 

 brown of various shades, and black, (ireen alone is absent from the list, 

 with ihe exception of a dark shade of it, approaching to black. The blue- 

 coloured variety has a very pleasing effect, somewhat like that produced by 

 the Wedgwood-ware, which has white figures on a blue ground. This 

 variety also retains its colours perfectly if preserved in a portfolio, and not 

 being subject to any spontaneous change requires no preserving process. 

 These different shades of colour are, of course, so many diltVrent chemical 

 compounds, which chemists have not hitherto distinctly noticed. 



3. First Apjdicaliuns of /his Prucvss The first kind of objects which I 



attennpted to copy by this process were flowers and leaves, either fresh, or 

 selected from my herbarium. These it renders with the utmost truth and 

 fidelity, exhibiting even the venation of the leaves, the minute hairs that 

 clothe the plant, &c. &c. 



It is so natural to associate the idea of hibutir with great complexity and 

 elaborate detail of execution, that one is more sliuck at seeing the thousand 

 florets of an A'jrostis depicted witli all its capillary branchlefs (and so accu- 

 rately that none of all this multitude shall want its little bivalve calyx, re- 

 quiring to be examined tlirough a lens), than one is by the picture of the 

 large and simple leaf of an oak or a chesnut. But, in truth, the difliculty is 

 in both cases the same. The one of these takes no more lime to execute 

 than the other ; for the object whicli would take the most skilful artist days 

 or weeks of labour to trace or to copy, is effected by the boundless powers of 

 natural clieniistry in the space of a few seconds. 



To give an idea of the degree of accuracy with wliich some objects can bo 

 imitated by this process, I need only mention one instance. Upon one occa- 

 sion, having made an image of a piece of lace of an elaborate pattern, I 

 showed it to some persons at the distance of a few feet, with the inquiry 

 whether it was a good represewtation V wlien the reply was, " Tliat they were 

 not so easily to be deceived, for that it was evidently no picture, but the piece 

 of lace itself." 



At the very commencement of my experiments upon this subject, when I 

 saw how beautiful were the images whicli were thus produced by the action 

 of light, I regretted Ihe more that they were destined to have such a biief 

 existence, and I resolved to attempt to point out, if possible, some method of 

 preventing this, or retarding it as much as possible. The following consi- 

 derations led me to conceive the possibility of discovering a preservative 

 process : — 



The nitrate of silver, which has become black by the action of light, is no 

 longer the same chemical substance that it was befoie. ('onsequently, if a 

 picture pioduced by solar liglit is subjected afterwards to any chemical pro- 

 cess, the white and dark parts of it will be differently acted upon ; antl there 

 is no evidence that, after this action has taken place, these white and dark 

 paits will any longer be subject t(fi a spontaneous change ; or, if the} are so, 

 still it does not follow that that change will ui^ir tend to assiniihne them to 

 each other. In cases of their reirraining cltssimihtr the pic ure will remain 

 visible, and therefore our object will be accomplished. 



If it should be asserted that exposure to sunshine would nrressnri/i/ reduce 

 the whole to one unilbrm tint, and destroy the picture, the omm ]>roba»di 

 evidently lies on those who make the assertion. If we designate by the letter 

 A the exposure to tlie solar light, and by B some indeterminate chemical 

 process, my argument was this: —Since it cannot be shown, u pnotiy that the 

 final result of the series of processes ABA will be the same with that 

 denoted by B A, it will be, therefore, worth while to put the matter to the 

 test of experiment, viz., by varying the process B luUil the right one be dis- 

 covered, or until so many trials have been made as to preclude all reasonable 

 hope of Its existence. 



My hist trials were unsuccessful, as, indeed, I expected; but after some 

 time I discovered a method which answers perfectly, and sliortly afterwards 

 another. On one of these more especially I have made numerous experi- 

 ments; the other 1 have comparatively little used, because it appears to re- 

 quire more nicety in the management. It is, however, equal, if not superior, 

 to Ihe first in brilliancy of effect. 



This chemical change, which I call the prv^riping process, is far more 

 effectual than could have been anticipated. Tlie paper, which had previ- 

 ously been so sensitive to light, becomes completely insensible to it, inso- 

 much that I am able to show the society specimens which have been exposed 

 for an liour to the full summer sun, and from which exposure the image has 

 suffered nothing, but retains its perfect whiteness. 



4, On Ihe All of fifing a Shallow. — The phenomenon which I have now 

 briefly mentioned appears to me to partake of the character of the viarcellons, 

 almost as much as Rny fact wliich physical investigation has yet brought to 



our knowledge. The most transitory of things— a shadow, the most pro- 

 verbial emblem of all that is fleetinj and momentary — may be fettered by 

 the spells of our " natural magic," and may be fixed for ever in the position 

 whicli it seemed only destined for a single instant to occupy. 



This remarkable phenomenon, of whatever value it may turn out in its 

 application to the arts, will, at least, be accepted as a new proof of the value 

 of the inductive methods of modern science, which by noticing the occur- 

 rence of unusual circumstances (which accident, perhaps, first manifests in 

 some small degree), and by following them up with experiments, and varying 

 the conditions of these until the true law of nature which they express is 

 apprehended, conducts us at length to consequences altogether unexpected, 

 remote from usual experience, and contrary to almost universal belief Such 

 is the fact, that we may receive on paper the fleeting shadow, arre.^t it there, 

 and in the space of a .single minute fix it tliere so firmly as to be no more 

 capable of change, even if thrown back into the sunbean from which it 

 derived its origin. 



.0. Before going further I may, however, add, that it is not always neces- 

 sary to use a preserving process. This I did not discover until after I had 

 acquired considerable practice in this art, having supposed at first that all 

 these pictures would ultimately become indistinct if not preserved in some 

 way from the change. But experience li.is shown to me that tliere are at 

 least two or three diftereut ways in which tlie process may be conducted, so 

 that the images shall possess a character of durability, provided they are kept 

 from the action of direct sunshine. These ways have presented themselves 

 to notice rather accidentally than otherwise ; in some instances without any 

 particular memoranda having been made at the time; so that I am not yet 

 prepared to sla'e .accurately on what particular lliiuf; this sort of semi-dura- 

 bility depends, or what course is best to be followed in order to obtain it. 

 But as I have found tlut certain of the images which have been subje«ted to 

 no preserving process remain quite whitt* and perfect after the lapse of a year 

 or two, and, indeed, show no symptom whatever of changing, while others 

 differently prepared (and left rmpreserved) have grown (juite dark in one 

 tenth of t'lat time, I Iliink this singularity reqiiirfsto be pointed out. Whether 

 it will be of much value I do not know. Pcrliips it will be thought belter 

 to incur at first the small additional trouble of employing the preserving pro- 

 cess, especially as the drawings thus prepared will stand the sunshine ; while 

 the unpreserved ones, however well they last in a portfolio or in common 

 daylight, should not be risked in a very strong light, as they would be liable 

 to change thereby even years after their original formation. This very 

 quality, however, admits of useful application. For this semi-durable paper, 

 which retains its whiteness for years in the shade, and yet suft'ers a change 

 whenever exposed to the solar light, is evidently well suited to the use of a 

 naturalist travelling in a distant country, who may wish to keep some memo- 

 rial of the plants he finds, without having the trouble of drying them and 

 carrying them about with him. He would only have to lake a sheet of Ibis 

 paper, throw the image upon it, and replace it in his portfolio. The defect 

 of this particular paper is, that in general the (/round is not even ; but this 

 is of no consequence where utility alone, and not beauty of effect, is 

 consulted. 



0. I'orlroils. — Another purpose for which I think my method will be 

 found very convenient, is Ihe m.aking of outline portraits, or sillii.iulles. 

 Tiiese are now often traced by the liand from shadows projected by a candle. 

 But Ihe hand is liable to err fronr the true outline, and a very small deviation 

 ciiuses a notable diminution in the re.semlilance. I believe this manual pro- 

 cess cannot be compared with the truth and fidelity with which the portrait is 

 given by means of solar light. 



7. Pointings on Glass. — The shadow- pictures which are formed by ex- 

 posing paintings on glass to solar light are very pleasing. The glass itself, 

 around the painting, should be blackened; such, for instance, a; are often 

 employed for the magic lantern. The paintings on Ihe glass should have no 

 blight yellows or reds, for these stop the violet rays of light, which are the 

 only effective ones. The pictures thus formed resemble the productions of 

 the artist's pencil mure, perhaps, than any of the others. Persons to whom I 

 have shown them have generally mistaken llicm for such, at the same liiue 

 observing that Ihe stith- was new to them, and must^be one rather difiicult to 

 acquire. It is in these pictures only that, as yet, I have observed indications 

 o{ colour. I have not had lime to pursue this branch of the inquiry further. 

 It would be a great thing if by any means we could accomplish Ihe delinea- 

 tion of objects in their natural colours. I am not very sanguine respecting 

 the possibility of this ; yet, as I have just now remarked, it appears possible 

 to obtain at least some indication of variety of tint. 



8. .■Ipplictition to the Microscope I now come to a branch of the subject 



which appears to me very important, and likely to prove extensively useful, 

 the application of my method of delineating objects to Ihe solar microscope. 



The objects which the microscope unfolds to our view, curious and wonder- 

 ful as tlicy are, are often singularly complicated. The c\c, indeed, may 

 comprehend the whole which is presented to it in the Held of view ; but the 

 powers of the pencil fail to express these minutiaj of nature in their innumcra- 

 hie details. What artist could have skill or patience enough to copy them? 

 Or granting that he could do so, must it not be at the expense of much most 

 valuable lime, which might be more usefully employed? 



Contemplating the beautiful picture which the solar microscope produces, 

 the thought struck nic whether it might not be po-sible to cause that image 

 to impress itself upon the pjpcr, and thus to let Nature substitute her own 

 inimiiable pencil for the imperfect, tedious and almost hopeless attempt of copy- 

 ing a subject so intricate ? 



My first attempt had no success. Although Icliose a bright day, and fornied 



