188 



SCIENCE-GOSSIP. 



[August 1, 186 r. 



PHOTOGRAPHY. 



La Planchette Photographique is the name of 

 a new instrument invented by M. Arthur Chevalier, 

 which is now attracting] considerable attention in 

 Paris. A report on its application to military sur- 

 veys is being prepared to place before the Govern- 

 ment, and it is shortly to be tested in the presence 

 of the Emperor in the camp at Chalons.—/. W. W. 



Photography and Anatomical Science. — M. 

 Ch. Ilouget desiring to demonstrate conclusively 

 errors commonly prevailing with respect to the struc- 

 ture of muscular tissue, has applied photography to 

 the purpose with great success. He was induced to do 

 so by finding preparations of the muscles could not 

 well be preserved in the required condition ; that 

 drawings were disputed, and the possibility of intro- 

 ducing actual experiment cumbered with too many 

 difficulties and disadvantages. Pictures produced 

 by the objects themselves, with extreme rapidity, 

 unerring accuracy, and exactly at the chosen time, 

 were therefore the best things M. Rougct could 

 think of, and these he has produced. Some of the 

 microscopic photographs exhibited were stereo- 

 scopic, which added . greatly to their value. — 

 /. W. W. 



Permanent Photographs. — The use of the per- 

 oxide of hydrogen for eliminating from photographs 

 the last trace of the destructive hyposulphites, to 

 which we called attention in our last, has found 

 opponents. Mr. E. W. Hart points out, that as 

 the per-oxide of hydrogen decomposes when in 

 contact with gold or silver, and also contains hydro- 

 chloric acid (used for its preservation), he cannot but 

 regard its proposed use as dangerous if not certainly 

 destructive to the photograph. In reply, Mr. Daw- 

 son, of King's College, states that using the per- 

 oxide of hydrogen manufactured by Mr. Bobbin, 

 he found the trace of hydrochloric acid contained 

 in it to be so trifling that in a ten-volume solution, 

 which is the strength at which it is used, blue 

 litmus-paper remained unchanged. He also asserts, 

 as the result of careful experiment, that the pre- 

 paration does not decompose when in contact with 

 a silver print. Dr. J. Emerson Reynolds is also 

 conducting analyses connected with this subject, 

 the results of which he promises to make public. 

 At present he is inclined to believe that the 

 application of per-oxide of hydrogen to a print is 

 only another mode of giving it a wash in a very 

 weak solution of sulphide of sodium, and thereby 

 facilitating fading. Thus "doctors differ," — Tempos 

 omnia revelat,~J. W. W. 



Experiments on Iodide of Silver. — The na- 

 ture of that invisible image which light fixes on a 

 surface photographically prepared, is a mystery 



which has baffled the best efforts of our most per- 

 severing and distinguished physicists and chemists. 

 Mr. M. Carey Lea (British Journal of Photography) 

 described a series of experiments bearing on the sub- 

 ject, in the course of which many errors were demon- 

 strated, and some new evidence of great value made 

 clear. These tended to prove that pure iodide of silver 

 is not chemically affected by light ; that although, 

 when exposed to light, it yields an image capable of 

 development, yet the chemical composition of the 

 iodide remains unaltered. The true action has there- 

 fore yet to be determined, and the controversy still 

 continues between those who uphold the molecular 

 or physical theory, and those who still retain their 

 faith in the chemical theory. Some of the more 

 recent efforts in this direction are due to Dr. 

 Tleissig, and certain experiments, which seem to 

 show that pure iodide of silver exposed to light 

 under a pure aqueous solution of the nitrate releases 

 oxygen and renders the solution acid, are important. 

 —/. W W. 



Curious Pact. — In the course of some remarks on 

 the precipitation of silver, Mr. Carey Lea describes 

 a curious fact in relation to the colour of the de- 

 posited silver. He says, " A plate was covered with 

 a considerable thickness of ammonia nitrate solution, 

 to which was added a dilute solution of Rochelle 

 salt. The plate was then placed in sunlight and 

 left for some time. Reduction took place, and the 

 evaporation, which went on simultaneously, had 

 extended over about one half the plate, when it 

 was removed from the sunshine. It was then care- 

 fully washed. All that part of the metallic silver 

 on which the solution had been suffered to dry in 

 the sun was pure steel-grey, whilst that which was 

 removed still wet had a strong reddish bloom." The 

 contrast remained permanently, and evidently de- 

 pended upon some difference of molecular arrange- 

 ment. " It would be interesting to observe," says 

 Mr. Lea, in connection with this, "whether nega- 

 tives which are dried in the sun are not thereby 

 somewhat different from the same or corresponding 

 negatives dried in the shade; and, also, whether 

 positive proofs on paper could not be affected for 

 good or for evil by drying in the sun."—/. W. W. 



Temperature. — The following data are from the 

 "Times" of July ISth :— 



