443 



KDooiledge & SeleDtifie fleuis 



A MONTHLY JOURNAL OF SCIENCE. 



Conducted by MAJOR B. BADEN-POWELL, F.R.A.S., and E. S. GREW, M.A. 



Vol. III. No. 19. 



[new series.] 



JUNE; 1906. 



SIXPENCE NET. 



CONTENTS See page Vll. 



Astronomical 



Photography. 



Hints to Amateurs Regarding Apparatus 

 and Methods of Working. 



By Alexander Smith. 



III. — Development of Plates. 



There arc no operations in connection with photo- 

 y^raphy which admit of such varied methods ol treat- 

 ment as the development of dry plates. When these 

 were first introduced, the available developing- agencies 

 were confined to pyrogallic acid and ferrous oxalate of 

 potash, but year after year has added to the number, 

 and at the present time a beginner is well nigh be- 

 wildered with the variety of formuku which he finds set 

 down for his g-uidance in modern photographic text- 

 books. In addition to the long list of v\hat may be 

 regarded as standard solutions, platemakers issue 

 special formulae, which may presumably be supposed 

 to g-ive better results than any other for their particular 

 brand of plates, while the fact remains that for all 

 ordinarv purposes a g^ood standard solution will satis- 

 factorily develop almost any reliable bromide of silver 

 plate on the market. Many workers confine themselves 

 to one make of plate, which they develop with a 

 favourite formula, and, where the results are all that 

 could be dt sired, the best advice that could be given is 

 toadiiere to them, as they become acquainted by experi- 

 ence with all their little peculiarities, which they are able 

 to turn to the best advantage. It is not so much a 

 question of using any special developer for the plates of 

 any particular maker, as of varying the details of treat- 

 ment for different classes of subjects. Those engaged at 

 astronomical work have to deal with objects of a very 

 diversified character — from the noonday sun to the 

 faintest class of nebuhe. In the one case the result 

 aimed at is to obtain detail on a brilliantly lighted sur- 

 face, and in the other the outlines of the merest trace of 

 luminosity projected on a very slightly darker ba<'k- 

 ground. 



For |MiotogTaphs of tlu- solar image a slow plate 

 should, :is already indicated, always be seUcled, and 



the same remark applies to lunar and planetar}' work 

 where the driving; arrangements admit of giving the 

 requisite exposure. A developer made up to any 

 standard formula may be employed, but with strontjiy 

 lighted subjects a weak solution will be found to give 

 more satisfactory results than one of normal strength, 

 the plate being: allowed to lie a proportionately longer 

 time in the bath, .^fter carrying out many experiments 

 the writer gives preference to a glycin developer, which 

 has many excellent properties. It is always ready for 

 use with the simple addition of water, and the same 

 solution may be used repeatedly. It does not stain the 

 hands, has no injurious effect on the skin, and keeps 

 indefinitely. It admits of great latitude in exposure, 

 and for all scientific work where it is desired to secure 

 soft and delicate detail it is unsurpassed. It may be 

 used with equal success for the development of nega- 

 tives, lantern slides, or gas-light papers. It does not, 

 however, possess the vigour of pyrogallic acid or metol, 

 and, consequently, the duration of exposure should 

 always be ample, but, on the other hand, a satisfactory 

 negative can be quite readily obtained, although the 

 normal exposure has been very greatly increased. The 

 point to be kept in view is that the developing agent 

 must be of a suitable strength to take up tlie work 

 where the action of light left off, and if an exposure. of 

 10 or 20 times the normal amount has been given, a 

 satisfactory negative can be quite readily obtained with 

 a glycin developer by employing a diluted, or, what is, 

 perhaps, more preferable, an old solution which has 

 previously developed several plates. Developing agents, 

 such as pyrogallic acid, do not admit of the same lati- 

 tude in exposure, and, if toned down by the addition of 

 bromide, the effect is hard and delicate detail is lost. 



The following formula, which the writer has used for 

 a ninnber of years, can be confidently recommended : — 



Water ... ... 18 ounces. 



.■sulphite of Soda i,ogo grains. 

 Potash Carbonate 2,270 ,, 

 (ilvcin ... ... 1 oz. bottle. 



Dissolve in hot water in the order given. When cold 

 the solution should be filtered and put into well- 

 stoppered bottles. For use, add three ounces of water 

 to one of the concentrated solution for ordinary work, 

 and about five ounces of water for lantern slides or gas- 

 lig-ht papers. Certain brands of the latter require the 

 addition of a little bromide, but for other purpo.ses it 

 mav be dispensed with, or, at all events, used verv 

 sparingly. -Solutions which have become slower in 

 action after developing a few plates should not be 

 thrown away, as these may be afterwards utilised in 

 cases where the normal exposure can be readily in- 

 creased, and, as a practical illiistration of the keeping 



