October, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



253 



lliis figure to vary considerably, accordiiiij to the char- 

 acter of the plate. 



The discrepancies obtained in the results of measur- 

 ing plates similarly exposed and developed gave ir 

 three series of experiments 3.2, 2.2, and 6.0 per ceni. 

 as the greatest deviations from the mean density m 

 each case. These errors, due to the plates, were ob- 

 tained by the use of an emulsion specially coated on to 

 plate glass, but not by means of the apparatus the 

 authors have sinci constructed for coating experi- 

 mental plates. 



Concerning the velocity of development with ferrous 

 oxalate, the authors find 'that _(t_) the silver is deposited 

 at first with increasing rapidity, then more slowly, 

 tending to a limit that depends only on the exposure, 

 (2) the velocity is proportional to the concentration of 

 the developer, but that this relationship is liable tO' be 

 interfered with by the accumulation of the products of 

 the reaction in the film, (3) a soluble bromide reduces 

 the velocity, but the reduction becomes less as the 

 action proceeds, (4) as the bromide is increased in geo- 

 metrical proportion the velocity diminishes in arithmeti- 

 cal proportion, (5) hardening the film is without effect 

 on the velocity of either developing or fixing, even when 

 a four per cent, solution of formaldehyde was applied 

 until the film was insoluble in cold water, (6) the velo- 

 city of development varies with different plates, and 

 diminishes for a given plate as it gets older, (7) the 

 velocity depends mainly on the rate of diffusion of the 

 developer. 



Concerning the grains of silver and their disposition 

 in the film, the authors find that (i) by short develop- 

 ment the depth to which the image extends is inde- 

 pendent of the exposure (I suppose in the absence of 

 soluble bromides), but that finally it becomes a maxi- 

 mum for each exposure ; (2) by exposing through the 

 glass, still the grains most exposed begin to develop 

 first ; (3) the size of the grains increases during deve- 

 lopment until finally it is independent of the exposure ; 

 (■4) the addition of bromide causes a diminution in the 

 size of the grains. 



Many of these conclusions are in full agreement with 

 the everyday observatio'ns of photographers, and the 

 results of previous investigators. It will, however, 

 doubtless surprise many to learn that the velocity of 

 development and fixing is not affected by the harden- 

 ing of the film. 



Mr. Sheppard has also published in the Journal of 

 the Chemical Society for August a communication on 

 development as a reversible reaction, and on the re- 

 tarding action of soluble bromides. I have refrained 

 from referring to anything stated therein, because, as 

 the author says that it bears on many points in photo- 

 graphic practice, he will, doubtless, shortly indicate its 

 practical importance himself. But I would remark on 

 the fact that in using the word "reversible," he does 

 not appear to consider the difference between develop 

 able and non-developable silver bromide. The silver 

 bromide is reduced by the developer, because it is in the 

 developable condition, undevelopable silver bromide not 

 being reducible under the same conditions. When the 

 reaction is reversed, the resulting silver bromide would, 

 I suppose, not be likely to be in the developable state. 



The Royal Photographic Society. 



The annual exhibition of pliotoRrapIis was opened on tlie 20th of 

 September at the New Gallery Kegent Street, and will remain open 

 until October 2Sth. The large collection will be found of considerable 

 interest to photographers. Amongst other items of scientific 

 interest are some fine specimens of X-ray work, and some examples 

 of three-colour printing. 



ASTRONOMICAL. 



By Charles P. Butler, A.R.C.Sc. (Lond.), F.R.P.S. 

 Nova. Aquilae. No. 2- 



In a telegram circulated from the Kiel CentralstcUe, Pro- 

 fessor Pickering announced tiiat Mrs. Fleming had discovered a 

 new star from examination of plates obtained at the Harvard 

 College Observatory. The star was situated near X Aquilae, 

 and was stated to be fading rapidly at the time of discovery, 

 September i. 

 The position first circulated was 



R.A. = 284° 2' = i8h se-i-". 

 Decl. = - 4° 34' ; 

 but a later wire gave a more accurate value of the right ascen- 

 sion as R.A. = i8h 57m 8s. 



Hy September 4 several visu.al observations had been made. 

 Professor Max Wolf reported that at Heidelberg the star was 

 observed on September 4, the magnitude being then about (y^. 

 The position was determined to be : — 

 R.A. = 18^5411245 ) (Epoch 1855). 

 ^ , 1, „ I 1905, Sept., 4'* 9*1 30"! Koenigstuhl 



Decl. = - 4" 39- J ii'ean Time. 



On September 6. Dr. P. Guthnick telephoned that he had 

 been able to observe the new star at the Bothkamp Observa- 

 tory, and giving its position to be : — 



18 54 25 

 iS 57 4 



4 3S-8 

 4 348 



1855-0 

 19050 



The magnitude on September 5 was about 10-2, and the 

 colour greenish yellow. 



Beginning of the New North Polar Cap 

 of Mars. 



An interesting observation was made at the Lowell Observa- 

 tory, Flagstaff, Arizona, on May ig, 1905, 'which determined 

 the' important fact of the definite time of formation of the 

 new north polar cap of the planet Mars. A large white patch 

 was first noticed south and west of the old polar cap, and it 

 was quite certain that nothing of the kind was visible the 

 day before. The season would correspond to that about 

 August 20 with us. In extent the area of the new patch was 

 enormous. On the 20th the white patch was again visible 

 and showed a brilliant kernel at its southern end in longitude 



+ 70". 



The date of this formation was 126 days after the summer 

 solstice of the Martian Northern Hemisphere, and it is very 

 important to note the agreement of this value with that 

 first determined in 1903, which was given at 128 or 129 days 

 after the northern solstice, as this shows evidence of constancy 

 of meteorological cycles on the planetary surface. 



Further Observatiorvs of Jupiter's 

 Seventh Satellite. 



From a telegram circulated by the Kiel Centralstelle, we 

 learn that Professor Albrecht has obtained another determi- 

 nation of the seventh satellite of Jupiter, with the Crossley 

 Rellector of the Lick Observatory, as follows : — 



Position Angle. Distance. 

 1905, Aug. 796 G.M.T. .. 2S9°-7 .. 54' 6 



In the Lick Observatory Bulletin. No. 82, a set of elements 

 for the satellite are given by F. E. Ross, computed from the 

 observations by I'errine, on January 3. February 8, and 

 March 6, 1905. 



