SCIENTIFIC SUMMARY. 
291 
never brought under the protecting influence of sunlight. An observation 
which points to the same conclusion, is the greater degree of permanence 
manifested by such prints as are freely exposed to air and light in shop- 
windows, as compared with the condition of others kept for stock in port- 
folios. The exceptions to this rule of general experience are rare, and 
appear to be such instances only as are obviously favoured by the main- 
tenance of a high temperature or unusually dry atmosphere in their 
vicinity, and where, consequently, the proportion of hygroscopic moisture 
absorbed by the prints, their paper mounts, and adhesive backing, is 
reduced to a minimum. 
The composition of the photographic image has again been brought 
prominently into notice by the lecture delivered by Mr. Malone on the 
occasion already alluded to (December 2nd, 1862). The experimental 
facts urged in favour of the truly metallic nature of the darkened particles 
which constitute the shadows of the picture, were based upon the result of 
exposing to sunlight a solution of ammonio-nitrate of silver, which had by 
repeated use become contaminated with sundry organic matters derived 
from the paper. The product was very similar to that before obtained by 
Mr. Spiller in working upon chloride of silver in an extremely fine state 
of division ; there was no doubt that the dark grey particles were com- 
posed entirely of metallic silver, since they imitated all the reactions of this 
elementary substance, and remained insoluble and unaffected by the 
several chemical agents usually employed in the process of fixing the 
photographic image. 
The Council of the London Photographic Society have decided on giving 
prize medals at the next exhibition of the Society. It is believed that 
four silver medals will be awarded : one for the best landscape ; one for 
the best portrait ; one for the best example of photographic art, whether 
a composition, picture, or copy of a work of art ; also, for discovery or 
excellence of manipulation. The exhibition will probably be held at the 
Suffolk Street Gallery early in 1863. 
The Marseilles Photographic Society have appointed a commission to 
inquire into the practical value of a suggestion made by M. Megnier, to 
employ the sulpho-cyanide of ammonium as a fixing agent in photography. 
The aqueous solution of this salt is said to dissolve the chloride and iodide 
of silver as freely as does hyposulphate of soda, at the same time not 
being liable to permit the formation of the black sulphide of silver on 
standing at rest, or by contact with the free nitrate on the surface of the 
print. 
A proposition of great importance has, during the past three months, 
occupied a large share of attention on the part of practical photographers. 
It has reference to the use of certain gum-resins for the purpose of im- 
parting to paper a close texture and lustrous surface, which qualities have 
hitherto been secured only by the use of albumen. Our most eminent 
photographic artists have long agreed in condemning the use of albumenized 
paper, as being altogether unsuited to the representation of many subjects, 
on account of the excessive and often objectionable glaze apparent on such 
prints ; its employment seemed however, virtually, a necessity, from the 
difficulty of rendering by other means the details in shadow. The all but 
