5^4 



KNOWLEDGE & SCIENTIFIC NEWS. 



[October, 1906. 



Photography. 



Pure and Applied. 



By Chapman Jones, F.I.C, F.C.S., Ac. 



Pholographic Exhibitions. — The annual exhibition of 

 the Royal Photographic Society at the New Gallery, 

 121, Regent Street, is now open, and will close on the 

 27th of October. All sections arc of interest and are 

 well represented, but we naturally turn to the techni- 

 cal section. The preponderance of photographs of 

 birds continues, if it does not increase. Nature, as we 

 know it, does not consist chiefly of birds, but one or 

 two indefatigable workers appear to have set the 

 fashion in this direction, and a considerable number of 

 photographers, the most of them less skilful tlian their 

 leaders, ha\e followed in the groo\e. The time is 

 past for showing an isolated photograph of a bird, un- 

 less it is a very rare specimen or has some very special 

 reason for its exhibition. Mr. W. Farren's series of 

 twenty-four photographs, showing the life history of 

 the stone-curlew, and Miss E. L. Turner's grebe series, 

 are highly commendable. A few years ago, similar 

 series, illustrating the growth of certain plants were 

 shown, but this year Mr. A. W. Dennis contributes a 

 series of a different kind. He illustrates wych elms, 

 and fine examples of them, in their different conditions 

 as to seasons, and also, on suitable scales, the various 

 details of their parts, such as the winter buds, the leaf, 

 the blossom, the fruit, etc. A most interesting exhibit 

 to those whose knowledge of the aberrations of lenses 

 is not very precise, is a series of models made by Mr. 

 \\'elbourne Piper, that clearly illustrate the paths of the 

 rays under various conditions by means of threads of 

 different colours. There are nearly three dozen models 

 on the six frames. For this new departure in the illus- 

 tration of the effects of lenses that are of prime impor- 

 tance in photography, the judges have awarded a 

 medal. We look in vain for any evidence of progress 

 in the department of colour-photography. The best 

 of the examples are not better than what has been seen 

 before. An invitation collection includes recent work 

 from the Greenwich Observatory and the Solar Physics 

 Observatory, Dr. W. J. S. Lockyer's series of cloud 

 photographs, a large series of photographs of electrical 

 discharges by Mr. K. J. Tarrant, further work by Mr. 

 Edgar Senior on the Lippmann method of colour photo- 

 graph}-, and other exhibits of much interest. In the 

 North Room there are several examples of " ozo- 

 brome " prints, with the bromide prints from which 

 they have been produced. 



There are two other exhibitions now open in London 

 that are of great interest to those who photograph, 

 though not from a scientific point of view. The 

 " Photographic Salon," at the Gallery of the Royal 

 Society of Painters in Water Colours, 5a, Pall Mall 

 East, is devoted entirely to pictorial work, and closes 

 on the 27th October. .A collection of portraits by 

 the late Mrs. Julia Cameron, and by her son, !Mr. H. 

 H. Hay Cameron, will be on view till the 6th of 

 Octoljer, at 24, Wellington Street, Strand. These 

 pictures of Mrs. Cameron's include some of the finest 

 photographic portraits (and one might perhaps almost 

 omit the word " photographic ") ever produced, and of 

 the finest subjects, for there are portraits of Carlvle, 

 Tennyson, Browning, Longfellow, Darwin, Sir John 

 Herschell, Joachim. Watts, and Miss Ellen Terry at 

 the age of seventeen. 



The Purchase of Photographs.— The. greater number 

 of the photographs in the exhibitions above referred to 

 can be purchased, as is usual in picture exhibitions. 

 During the last ten years, or rather more, it has become 

 fashionable to omit all reference to the nature of 

 pictorial photographs, that is, what the image consists 

 of, or how it has Ijeen produced, for fear, I suppose, 

 lest they should be bought as sjx'cimens of processes 

 instead of because of their pictorial merit, or for fear 

 the artist should feel handicapped in their production, 

 not always knowing himself what his methods lead to. 

 There are many photographers who take great care 

 that their pictures contain nf)thing but what may 

 fairly be called permanent, but others are not so 

 scrupulous. \ fine effect may l)e obtainable in fugitive 

 material, and through ignorance or indifference they 

 avail themselves of a process or a detail in the process 

 that they ought to absolutely shun in any picture that 

 is offered for sale. -As the possible \ariations in photo- 

 graphic methods are more numerous than in any other 

 current method of pictorial expression, this reticence 

 is a distinct disadvantage to the would-be purchaser 

 and doubtless also to the photographer. 



Colour Photography. — Professor Lippmann has re- 

 cently described in the Comptes Rendus, another method 

 of colour photography. .\ plate that is opaque, except for 

 fine parallel lines, about 125 to the inch, is fixed at one 

 end of a light-tight box, a photographic plate is at the 

 other end, and a lens between is so arranged that it 

 forms a sharp image of the grating on the plats. A 

 small angled prism is fixed near the lens so that the 

 light that passes through each line (as through the slit 

 of a spectroscope), is dispersed into a spectrum, hut so 

 ^;hort a one that it only just covers the otherwise blank 

 space between the image of one light line and the next. 

 Instead, therefore, of a series of separated fine lines 

 on the plates, the surface is covered with lines of 

 colour, very much as if a Joly compound colour screen 

 were in front of it, but there is a spectrum instead of 

 L-ach group of three coloured lines. An image of the 

 coloured object that is to be photographed is projected 

 by ordinary optical means on to the grating, the ex- 

 posure is made, and the plate developed. By putting 

 (1 suppose) a positive, made from the negative in 

 exactly the place occupied by the negative durine )he 

 exposure and illuminating it with white light, a 

 coloured image, similar to the one photographed, will 

 be produced in the plane originally occupied by the 

 grating. It is obvious that the ultra-violet must be ex- 

 cluded, the plates must be sensitive to the whole of the 

 \isible spectrum, and other precautions must be taken 

 that need not be enumerated. It is a pretty and inter- 

 esting method that must need very nice manipulation 

 to ensure succ-ess. 



Colour-Scusitised Plates. — Messrs. Wratten and \\'ain- 

 wright send us a sample of their " .Allochrome " plates, 

 which are sensitised for green and yellow, but not for 

 red, and are thus comparable with the colour-sensitised 

 plates that are best known and made by many 

 makers. The sample is of excellent quality and backed 

 with a black backing that does not detach itself, but is 

 easily removed when done with. This, with the plates 

 referred to before, makes a very complete series, and 

 a booklet that the firm have just issued describes the 

 many kinds of plates that they make, including five 

 varieties of plates specially sensitised for colour, and 

 gives advice as to their use. Colour screens or filters 

 of various kinds and of three densities, specially suit- 

 able for use with the plates, and others for three-colour 

 work, are issued by the firm. 



