62 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Mak., 1905. 



of the phenomena preceding spark discharge, I had occasion 

 to make many electrographs showing the field between the 

 electrodes of the gap in the various stages of the strains 

 breaking down the di-electric strength of the air. The en- 

 closed are two of them. One shows the invisible brush which 

 evolves just before the spark passes — the other is of the tenta- 

 tive feelers being emitted by the positive prior to the formation 

 of the negative component. 



As there is a considerable field open to experimenters in this 

 direction you may care to publish these electrographs. 

 Vours faithfully, 



Alfred Williams. 

 Laboratory. Meadow House, Ealing, W.. 

 February 6, 1903. 



Photography. 



Pure arvd Applied. 



By Chap.man Jones, F.I.C, F.C.S., &c. 



Time Development. — This means the treatment of ex- 

 posed plates to a prepared developer for a fi.\ed time, 

 which may have to be varied a little according to the 

 temperature and will not be the same for difTerent 

 developers or plates of difTerent makes, but which is not 

 varied to suit the subject or the e.\posure. The plates 

 are put into the developer for the specified time and then 

 fixed and washed without inspection. The \ise of the 

 Kodak developing machine renders the following of this 

 method obligatory, for inspection during development is 

 then impossible. There are modifications of time 

 development that allow for variations of temperature and 

 certain changes in the developer, but I refer now to the 

 simple method just stated. 



There has been considerable argument and some dog- 

 matic e.xpressicn of opinion as to whether time develop 

 ment is advantageous, whether, indeed, there is any 

 advantage in any other method. The case in favour of 

 it was very strongly set forth by Mr. R. Child liajley, a 

 week or two ago, in a lecture at the Society of Arts, and 

 the Chairman, Mr. George Davison, emphatically sup- 

 ported the lecturer, showing prints from negatives of the 

 same subject that had received exposures of 1,2, 4, and 8 

 units of time, and had been developed together for the 

 same time. The longer the exposure the denser the 

 negative and the longer the exposure required for print- 

 ing from it, but the prints from these negatives were all 

 satisfactory and not very different from one another. 



The advantages of such a mechanical method of 

 development are obvious. There is no light fogging — 

 for the plate may be kept absolutely in the dark ; the 

 fingers are not dabbling in the solution — for the plate is 

 not removed from the dish until the time is up ; all 

 doubt as to when development is complete is removed — 

 for any one can read a clock though few can tell by in- 

 specting an unfixed plate whether the image is satisfac- 

 tory ; in the Kodak machine a whole roll of exposures is 

 developed at once, so that much time is saved ; and all 

 risk of damage to the film is obviated because it is per- 

 fectly supported and not touched during development and 

 fixing. The question is what do we give up for these 

 very notable advantages ? Some say, Nothing, and that 

 what we imagine we lose is merely a matter of fancy or 

 sentiment. With regard to the vast majority of those 

 who develop photographs I believe this to be absolutely 

 true, and that the net result of adopting such a method 

 would be found to be a considerable gain in the 



quality of the resulting negatives. But I also doubt 

 whether there are more than perhaps one in ten thousand 

 of those who do a little drawing find painting whose 

 drawings are worth as much as an ordinary photograph of 

 the same subject, and the fact that few excel is no proof 

 that i:one do or that it is impossible to excel. I am 

 con\inced that the same is true with regard to develop- 

 ment, and that with knowledge and practice, constant 

 practice, that is, not merely the developing of a batch or 

 plates three or four times a year, results may be obtained 

 that mechanical methods could not give. This leads to 

 another <]uestion : Is it worth while even for this excep- 

 tionally able and practised worker to bestow so much 

 trouble in personal and detailed attention when the tim- 

 ing method gives such an excellent yield of good results ? 

 I very much doubt whether it is unless he is engaged on 

 exceptional work. 



It will be understood that these remarks are intended 

 to apply to ordinary photography as it is commonly 

 understood. But I have no doubt that much scientific 

 photography would yield a belter average of results with 

 less trouble if development were simply timed. For 

 exactly repeating definite results, the timing method 

 (using the same developer at the same temperature) is the 

 only way to justify the anticipation of success. 



Improvements in Colour-Photography. — Messrs. Sanger- 

 Shepherd and Co., who have done so much to make 

 photograph}' in colours possible for any one who can 

 photograph at all, are introducing some notable improve- 

 ments in apparatus and methods. The repeating- iiack 

 camera is still to be preferred for subjects that permit of 

 consecutive exposures for the three negatives (the red, 

 green, and blue records), but the advantages of a camera 

 that gives the three negatives side by side on the same 

 plate by one exposure are so obvious that they do not 

 need pointing out. Such a camera they have just per- 

 fected. It has only one lens, so that the triple exposure 

 needs no more manipulation on the part of the photo- 

 grapher than if he were using any ordinary camera. 

 This means that there remain now no limitations in ihe 

 character of the thing or scene photoRraphcd other than 

 exist in ordinary non-colour photography, except that, 

 other things being equal, the exposure for the colour 

 photograph must be rather longer. Hut with the plates 

 now in use the length of exposure is very moderate. I 

 have seen a very good portrait of a dog which was taken 

 in ten seconds. The camera is compact, being no 

 larger than necessary to carry the plate in two directions, 

 and the size in the otiier direction is no more than 

 sufficient to carry the lens in the front and the plate at 

 the back as in ordinary apparatus. A very con\enient 

 size takes the half of a half-plate, divided longitudinally, 

 and a larger size the third of a 10 by 8 plate. 



The same firm will shortly have on the market a 

 bathed plate — that is, a plate sensitised for colour after it 

 is made instead of being coated with an emulsion already 

 sensitised. The great advantage of such plates has long 

 been known, but 1 believe that they have not before been 

 obtainable commercially. The advantage is that they 

 are so much more sensitive to red and green that the 

 exposures for these colours are not very different from 

 that needed for the blue image. Such plates in the 

 camera mentioned above will require an exposure of only 

 one second instead of about fifteen for average subjects, 

 an advantage that will at once be appreciated by all 

 practical photograjjhers. With such an exalted sensitive- 

 ness to red, the plate has to be developed in the dark, 

 unless the photographer knows how, by keeping his dis-h 

 covered, and so on, to avoid light fog. The plates give 

 very clean and bright negatives. 



