1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



101 



and opposite in effect tu all other water-mixed cenunls. There is neither 

 heat nor expansion in solidification, nor subsenuenl swelling from absorption 

 of the atmosphere or hy immersion iu water. It thereliae results that the 

 cement neither cracks nor creases, wiicn nscd either as an in or out-door 

 stucco. The mode of using the cement is verj' simple — similar to common 

 lime pla«ter, but tJic purposes lu Avhich it is applicable are extremely 

 varied. .As it can be made of a variety of colours in manufaclme, or 

 Colours introduced, it will sojjersede the necessity of paint or pnper, where 

 their use is objectionable ; il is theret'ore particularly applicable fur attics 

 and basements. 



For imitations of marble it must beci.nu' the substitute of jilaster of 

 Paris, il being much more dense, and throup:Ii its nonabsorptive qiialily 

 withstanding all atmospheres, as has been already pro\ed. As il dues nut 

 expand in solidilication, as abo\ e slated, solid figures may be cast witli it 

 if pressed into moulds. It cuinliines readily ■niih limes slaked m- quick, 

 and mixed with the latter it prevents its slaking, and with these, or by 

 itself and sand, it forms an excessively hard and durable stucco. In ils 

 prepared slate fur use it docs not receive the slightest injtiry fniin exi>osurc to 

 a damp atmosphere for any length of period, and will tliercforc carry 

 without depreciation to any part of the globe — it is effective for every 

 pm-pose for which the limes of iliis kingdom are used in its transatlantic 

 possessions; and from being double their weight, \\ill be nearly as 

 economical in use, iiulependent of ils pei-uliar properties excluding all 

 moisture and preM;nting the intrusion and ravages of insect and other 

 vermin: coubideratiuns not only important to the resident, but to the 

 government as conservators of the public stores. 



For the joining together of stones, bricks, &c., it lias not ils enual, and 

 can be used with the greatest ad\antage, where lime proves but an 

 insufficient bond, and Roman ccmeni IVurn its expansive properties is 

 improper; say for light-houses aiul ollii'i very eliiated and much-exposed 

 stnictures. 



-Applied .as a stucco over common lime plaster a very smooth and hard 

 surface is produced, and is so little absorbent that in painting two coals 

 ai'c sufficient. Tliis application was made by Mr. Chadwick above three 

 years since, on two halls at .\dclaide-]ilace, London Bridge, and who will 

 verify the fact here staled. 



In the summer of 1837 il was applied iu castings and as a stucco, at 

 72, Cheapside (opposite the .\tlas Insurance Office) ; the stucco lias been 

 since painted over, but not so the two coats of arms, which, as well as the 

 stucco, have ^^ithstood the two last winters without the slightest injury. 



.\ny further information respecting properties, &c., &c., may be obtained 

 of Mr. Bernasconi, Alfred-place, Bedford-square, and who will also show 

 specimens of its ^■ariou3 ajiplications. 



PHOTOGENY ; 



OR, THE tRT OF FIXING THE IM lOES OF VI.SUAF. OBJECT.*!. 



The means of olitnining a self-aeling, permanent repvesciitation of 

 visual objects, has long attracted the attention of philosophers, and 

 in 1802 was the subject of experiments by Wedgewood and Sir 

 Humphry Davy. Their eflort.s, further than recognising the sensi- 

 bility of nitrate of silver, weie, however, ineH'cclivc, as were those 

 of a connnittee of the Ac,^delny of Sciences, composed of Laplace, 

 Malu.s, and Arngo, who were engaged in a similar manner investiga- 

 tion for ascertaining the power of moonlight. Chlorure of silver 

 was also known to be easily acted upon by the rays of light ; but it 

 was not until the close of last year that any announcemenl was made 

 of the progress of this art. Mr. Fox Talbot seems to have been first 

 in the field; but M. Daguerre, the inventor of the diorama, made 

 the first disclosure. As the two processes seem to be distinct iu their 

 results, we sliall give a description of each separately, as deri\cd 

 from the " Compte Rendu '' of the Academy of .Sciences, and from 

 the letters of Mr. Talbot. To commence with that of M. Daguerre, 

 it i.s effected by placing a copper plate in a camera obsiuira, wliicli 

 copperplate being covered with a chemical preparation susceptible 

 of the etl'ccts of light, produces a .shaded drawing on the jdale. 

 Those designs, when finished, may be exposed to the glare of the 

 sun without changing, and will bear the scrutiny of a microscoi e. 

 On reverting to the difi'erent powers of colours, it can be readily 

 C(mceived that the several tints and shades will produce an efl'ect 

 corresponding to their intensity ; the tlirce primitive colours, as 

 determined by Field, standing in the relation of three, five, and 

 eight; the time required for the process varies with the quantity of 

 light, and, consequently, with the season and time of day ; in sum- 

 mer, at noon, eight or ten minutes is sufficient. This apparatus is 

 at present incompetent lo the representation of moving objects, and 

 is imperfect even with regard to trees. A hackney-coach stopped 

 during the drawing of one of the scenes, and one of the horses, 

 turning his head during the process, is represented without one. 

 a shoe-black, also engaged in his vocation, appears without .irms ; 

 The Academy of Sciences expressed a unanimous opinion of the 

 utility aiul importance of this invention, and application has been 

 made to tlie French Government to remunerate the inventor. Tlie 

 aniioimcement of this discovery led to the declaration of Mr, Fox 



Talbot, who has perfected another variety of the same process. He 

 uses a prepai'ed paper, and produces a representation in coloured 

 tints, which, after the drawing is finished, is not aft'eeted bv sunshine. 

 Both processes pos.scss peculiar advantages, and have a superiority 

 over any chemical medium heretofore known. Chlorure of silver 

 being while, is blackened by the light, and the white parts of the 

 image become black, wliilst the black parts remain white. Nitrate 

 and muriate of silver obtain an impression iu half a second, but -cvone 

 of these preparations iiroduce a pennanent efiect. The impoitance 

 of the new discoveries will open a new world to science, and even 

 by the results already produced, the bounds of human investigation 

 have been enlarged. The preparation of M. Daguerre is so sensible 

 t hat it has obtained an image of the moon in twenty minutes, although 

 the light of tliat body is 300,00(j times less than that of the sun, and 

 it produces no eflfect im any oilier chemical substance yet known. 

 M. Daguerre is also said to liave obtained an impression from the 

 star Sirius, thus proving the fixed stars to be suns, and that light is 

 homogeneous throughout the universe. 



We cojiy the following very interesting account of the process 

 of Mr. Talbnt from our respectable contemporary, the " Athenojum " : 



I. In the spring of 1S34 I hegau to pnl in |iractice a method whirb I had 

 devised some time previously, for employing to purposes of utility the very 

 curious property which has been Inug known to chemists to ba possessed by 

 the nitrate of silver ; namely, its discolouration when exposed to the violet 

 ray of light. This property appeared to me to be, perhaps, capable of useful 

 application in the following manner: — 



1 proposed to spread on a sheet of paper a sufficient quantity of the nitrate 

 of silver, and then to set the pa])er in tfiesun.shine, liaving first placed before 

 it some object easting a well-defined shadow. The light, acting on the re^t 

 of the paper, would naturally blacken it, while the parts in shadow would 

 retain their whiteness. Thus 1 expected that a kind of image or piotuie 

 would be produced, resembling to a certain degree the object from wbieh it 

 was derived, 1 expected. howe\'er, also, that it would be neeessai>' to pre- 

 serve such images in a portfolio, and to view them only by candle-light ; 

 because, if by d.iy-lighl, the same natural process which formed the imagej 

 would destroy them, by blackening the rest of the paper. 



.Such was my lending idea before it was enlarged and corrected by experi- 

 ence. It was not until some time after, and when I was in possession of 

 several novel and curious results, that I thought of inquiring whether this 

 pine.ss bad been ever proposed or allempted before? I found that in fact it 

 h.id ; but apparently not followed up to any extent, or with much peise- 

 veranee. The few notices that I have been able to meet with arc vague and 

 unsatisfactory, merely stating that such a method exists of obtaining the 

 outline of an object, Imt going into no details respecting the best and most 

 advantageous manner of proceeding. 



The only definite account of the matter which I have been able to meet 

 with, is contained in the first volume of the " .lournal of the Royal Insti- 

 tution," page 170, from which it. :ippe,ars that the idea Wiis originally started 

 by Mv. Wedgwood, and a numerous series of experiments made both by him 

 and Sir Humphry Davy, wdiicb. however, ended in failure. I will take the 

 liberty of quoting a few passages from this memoir. 



" The copy of a painting, immediately after being taken, must be kept in 

 an obscure place. It m.ny. indeed, be examined in the shade, but in this 

 case the exposure should be only for a few minutes. No attempts that iiave 

 been made to prevent the uncoloured parts from being acted upon by light 

 have .as yet been successful. They have been covered with a thin coating of 

 fine vainish ; but this has not destroyed their susceptibility of becoming 

 coloured. When the solar rays are passed through a print, and thrown upon 

 prepiired paper, the unshaded parts are slowly copied ; but tlie lights trans- 

 mitted br the shaded parts are seldom so definite as to form a distinct resem- 

 blance of them hy producing dift'erent intensities of colour. 



" The images formed by means of a cai/iera obscKra have been found too 

 faint to produce in any moderate time an effect upon the nitrate of silver. 

 To copy these images was the fir.«t object of Mr. Wedgwood, but all his 

 numerous experiments proved unsuccessful." 



These are the observations of Sir Humphry Davy. I have been informed 

 liy a scientific friend th.at this unfavourable result of Mr. Wedgwood's and 

 Sir Humphry Davy's experiments was the chief cause which discouraged him 

 from following up with per.seveiauce the idea wliich he had also enlertained 

 of fixing the beautihil images of the rainiin olisciirii. And, no doubt, when 

 so distinguished an experimenter as Sir Humpliry Davy announced "thai 

 all experiments had proved unsuccessful," snob a statement was calculated 

 materially lo discourage fuitber inquiry. The circumstance, also, announced 

 by Davy, that the paprr on which these images were depicted was liable to 

 become entirely dark, and thai nothing hitherto tried would prevent it, would 

 perhaps have induced me to ( onsider the attempt as hopeless, if I had not 

 (fortiuiately), before I read il, already discovered a method of overcoming 

 this diflficuiiy, and of //.//«// the image in such a manner that it is no more 

 liable lo injm-y or destruction. 



In the course of my experiments directi d to that end, I have been 

 aslouiihed at the variety of effects which I have found produced liy a very 

 limited number of difti rent processes when combined in various \v:iys ; and 

 also at the length of time which sometimes elapses before the full effect of 

 these manifests itself with certainty. For 1 have found tliat images formed 

 in this manner, which have appe.ired in good pr«serv."ition at the end of 



