466 



KNOWLEDGE 



[MAUcn 31, 18b2. 



PTTOTOn RAPHY FOR AMATEURS. 



i;v A. liiioTirEHS, F.R.A.S. 



FEW sul)J<'ots connected with science present more points 

 of interest tlian the discovery of pliotograpliy. M. 

 Niopce, OS we liavc; seen, Inlwured most patiently for many 

 years, and only achieved partial success. Independently, 

 Dap;uerre was working with a similar oUJect — that of iixing 

 the image produced by light wlien projected by means of a 

 lens on to a sensitive chemical compound. Also indepen- 

 dently, Mr. H. Fo.\-Tall)ot commenced experiments for 

 li.xing the photognphic imago. In his work, "The Pencil 

 of Nature," Talbot relates that in 18;il, while sketching 

 the scenery of Lake Como by means of the camera lucida, 

 the idea occurred to him that it ought to he possible to fi.x 

 the image produced by light by chemical means ; and on 

 his return to England he commenced researches, and con- 

 tinued them witli such success, that in 1839 he read a paper 

 before the Royal Society announcing his discovery, and in 

 18-lrl he secured his process by patent. This patent, how- 

 ever, he very generously resigned a few years later. 



In his " History and Handbook of Photography," Tis- 

 sandier i-elates a circumstance which I have not seen else- 

 where, and it deserves to be repeated, as it shows that 

 others besides those savants already named were busy try- 

 ing to solve the ditiicult problem of painting by sunlight. 

 The authority quoted is " Guide du Photographic," Paris, 

 1856, and the narrator of the fact is M. Chevalier, an 

 optician. Daguerre and others were in the habit of fre- 

 quenting Chevalier's shop, and in 1825 a young man 

 called to inquii-e the price of a new lens which he had 

 heard Chevalier was making. The price appearing to be 

 beyond the man's means, he was asked for what purpose 

 he wanted the lens, when he said that he had succeeded in 

 fixing the light-produced image. Chevalier thought " Here 

 is another of those poor fools who want to fix the image 

 of the camera obscura ! " But Chevalier was astonished 

 when the man placed a paper on the counter. " That," he 

 said, " is what I can obtain." Chevalier looked at it, and 

 was astonished to find a view of Paris as sharp as the 

 image of the camera. The inventor had fixed the \"iew of 

 Paris as seen from his window. 



Here was an instance of success achieved, but for want 

 of means, the discovery could not be carried further, and 

 when we remember the importance of the matter, it is 

 strange that the discoverer is never heard of again. 



It is unlikely that Talbot could have known what others 

 were doing, as it was seen, when the two processes were 

 compared, that they were totally difl'erent. Daguerre's 

 pictures were on polished silver, made sensitive with the 

 fumes of iodine. This image was latent ; that is, nothing 

 could be seen until the vapour of mercury was caused 

 to develope the image ; that is, the mercury was de- 

 posited in proportion to the action of the light on the 

 plate. Talbot's process was altogether different. The 

 image was produced on paper, and was a negative. The 

 advantage over the Daguerreotype in this case was that an 

 almost unlimited number of copies could be produced as 

 positives ; that is, prints haWng the lights and shades as in 

 nature. Both of these valuable discoveries were to some 

 extent due to accidents. Daguerre noticed the effect pro- 

 duced on a plat(! coated with iodine, on which an object 

 had been accid(!ntally placed ; and Talljot observed that 

 gallic acid, which had been spilt on his prepared paper 

 after exposure to light, developed the latent image. 



These are the main facts relating to the discovery of the 

 photographic art. and further detail here is unnecessary. 



1'ioth of the processes named were extremely slow, several 

 mitiut<'S being ncces.sai'y to produce a portrait. But im- 

 pro\('inents were rapidly made. After bromine was intro- 

 duced into the process by the late Mr. John Co<ldard, the 

 Daguerreotype plates were so sensitive to light, that a rapidly- 

 re\olving wheel was photographed while illuminated by an 

 electric spark — a feat which can scarcely be surpassed in 

 the present day. 



Many new, and modifications of old, processes were intro- 

 duced, but it remained for the late Mr. F. Scott Archer to 

 simplify and improve the method of obtaining the image 

 formed by light — the great improvement being the use of 

 glass to liear the film on which the image was to be fixed. 

 Various attempts had been made by the late Sir John 

 Herschel and others to utilise glass, but it was ilr. 

 Archer v.-ho succeeded with collodion — a fluid substance, 

 formed of gun-cotton dissolved in ether and alcohol. Archer 

 did not discover collodion, but used it as a vehicle to hold 

 iodides and bromides which were made sensiti^•e to light in 

 the way we shall see in a future paper. 



ti 



NOTES ON ROWING. 



By an Old Club Captaix. 



"1 T7HAT sort of stroke is necessary properly to drive at 

 * V racing speed the modem racing boat, is sufficiently 

 clear, as we have shown. How that stroke is to be given 

 remains to be considered 



I take it, there can be no room for doubt on one point 

 The old-fashioned rule, according to which the arms acted 

 merely as stretchers in the first part of the stroke — in fact, 

 untU the body became upright^ — can no longer be right A 

 stroke beginning under those conditions must necessarily be 

 sluggish at the beginning, and want the sharp grip or catch 

 which we have seen to be absolutely essential. On the 

 other hand, arm work alone at the beginning of the stroke is 

 utterly bad. But the stroke is taken with such sharpness, 

 to give the sledge-hammer blow necessary for propulsion in 

 the modern racing craft, that it is by no means easy, even 

 for the possessor of a perfect — that is, of the most effective 

 — rowing style, to say exactly how his work is dona Mr. 

 Muybridge's photographs of rapid movements by athletes 

 have shown that men who can accomplish some feat in 

 gymnastics, and even champions in such ordinary actions as 

 running and jumping, often have (^Ir. iluybridge, when I 

 was talking to him on the subject at San Francisco, said 

 they abrays have) the most incorrect ideas as to the way 

 in which they perform their feats. Accordingly, we must 

 not take it too surely for granted that because an oarsman 

 says he does this or tliat in taking his stroke, he necessarily 

 does so. Rapid photographs alone could tell us precisely 

 how the best oarsmen take the stroke ; but, for my own 

 part, I feel assured, as well from practical as from theo- 

 retical considerations, that while the l)ody is moving from 

 its most forward position to uprightness, the arms do so 

 much of their work that they are very considerably bent 

 by the time the body is upright. Many Oxford men say, 

 and doubtless believe, that in the Oxford style the arms 

 are not bent at all till the body begins to pass the upright 

 position. All Cambridge men know that at Cambridge 

 the old rule used to be regarded as absolutely to be 

 observed, that till the body was upright the arms should 

 do no work. At Cambridge the rule was rigidly followed. 

 In the Oxford style I feel satisfied, from repeated obserx-a- 

 tions, it is not followed ; and not a few Oxford men have, 

 on carefully studying the matter, admitted to me that this 

 is the case. 



