JANUARY 24, 1907] 
NATURE j 311 
the metastable limit of the silver solution be introduced, 
then the halide becomes developable. The following sub- 
stance 5s can act as germs for a dry plate :—(a) silver, 
intr tuced as colloidal silver and then converted to the 
me .ilic state; (b) gold; (c) platinum; (d) silver sulphide ; 
(e) gas ions from flame gases. 
All evidence tends to the conclusion that a necessary and 
sv ficient condition for ‘‘ developability ’’ is the production 
in the silver-halide grain of a new substance. The authors 
have accepted a chemical theory of the latent image chiefly 
on account of the way in which the latent image gives 
certain definite chemical reactions, and especially on 
account of the destruction of the latent image by oxidising 
agents. They have made an extended investigation of the 
destruction of the latent image by chromic ‘acid, with 
especial reference to the theory of primary and secondary 
development put forward by Mr. Sterry in January, 1904. 
This theory suggests that the primary image formed by the 
development of the “‘ latent ’’ image is intensified by silver 
transferred from other parts of the film. 
The authors found that exposed plates, dipped in chromic 
acid solution before development, have their y,, and inertia 
unaltered, but the development-velocity constant, K, lowered 
by the action of the chromic acid adsorbed to the silver 
bromide. This chromic acid was destroyed by sodium 
sulphite, and the plates then gave a normal K. If, how- 
ever, a plate was left after chromating, before develop- 
ment a fall in y,, was found which could not be destroyed 
by sulphiting, and which therefore showed an absolute 
destruction of the latent image. Probably this action was 
a re-oxidation process. 
The second part dealt with a peculiar action of salts of 
copper, iron, mercury, and uranium, which desensitise the 
plate, so that enormous exposures are required to produce 
normal results. If the plates are exposed and developed 
after desensitising, K and y, are found to be normal. 
If, however, the plates are left for a long period after 
exposing, then the desensitisers destroy the latent image 
by lowering y.. in the same way as chromic acid. 
The theory advanced for this action was that desensitisers 
act by catalysing the oxidation reaction, which is the 
opposite to the ordinary light reduction action, and this 
view was supported by experiments which showed that 
with copper, quinine salts, and with iron, oxalates re- 
stored the lost sensitiveness, a result analogous to that 
obtained for the negative catalysis of quinine in the case 
of the catalysis of sodium sulphite oxidation by copper 
salts. 
The authors have also repeated the experiments of Abney 
and Englisch upon the failure of the Bunsen-Roscoe 
reciprocity law, and of the integration of intermittent ex- 
posures. The results obtained agree with those previously 
found. The authors consider ripening to be due to the 
joint action of the (a) formation of resonating systems; 
(b) formation of reduction product, the function of the 
gelatin being to form resonators and to assist in reduction. 
The authors consider the formation of the latent image 
to be connected with the photoelectric effect, and to be due 
to the liberation of electrons which ionise the halide and 
the surrounding gas. This theory accounts for the action 
of dyes as sensitisers for their own region of absorption, 
since these electrons will ionise the halide effectually. 
Ionisation leads to chemical reduction, resulting in the 
formation of a subhalide in solid solution. 
Paris. 
Academy of Sciences, January 14.—M. A. Chauveau 
in the chair.—A comparison between chemical phenomena 
determined by a heating resulting from external calorific 
causes and those due to a heating produced by electrical 
actions: M. Berthelot. Stress is laid on the fact that 
changes undergone by a substance when heated by passage 
of an electric current cannot be entirely regarded as due 
to the thermal effect of the current.—The so-called artificial 
plants: Gaston Bonnier. An adverse criticism of a recent 
paper of M. Stéphane Leduc.—The eighth .campaign of 
the Princess Alice II.: The Prince of Monaco. A 
general account of the work done on Spitsbergen in the 
fields of geography, hydrography, meteorology, oceano- 
NO, 1943, VOL. 75] 
graphy, zoology, and physiology.—The critical points of 
inverse functions: A. Hurwitz.—The critical points of a 
class of functions: Georges Rémoundos.—The potentials 
of an attracting volume the density of which satisfies 
Laplace’s equation: Tommaso Boggio.—The movement of 
liquids with high velocity through very large conduits: 
H. Merezyng. Experiments on pipes of 38 ecm. and 
y . 
50 cm. diameter, the water flowing at rates between 
3 and 4 metres per second, gave results differing 
markedly from those obtained by an extrapolation from 
Darcy's formula. Experiments were also made on the 
quantities of sand carried in suspension by the water at 
different velocities—The importance of the thickening of 
the anterior edge of the wing of the bird in flight: appli- 
cation to aéroplanes: E. Seux.—A new wireless tele- 
mechanieal apparatus: G. Gabet.—The exact calculation 
of the moleeular weights of gases: Daniel Berthelot. A 
comparison of the results of the application of two methods 
of reduction of experimentally determined gas densities to 
the determination of the molecular weights of hydrogen, 
nitrogen, carbon, and chlorine in terms of oxygen = 32.— 
A sulphate of chromium the acid of which is entirely 
hidden, and on the equilibrium of chromic solutions : 
Albert Colson. The salt, the method of preparing which 
is described, has the composition Cr,(SO,),+6H,O. The 
solution of the salt reacts with barium chloride very 
slowly.—Dyeing and ionisation: Léo Vignon.—The action 
of silicon chloride upon chromium: Em. Vigeuroux. 
These two substances react at about 1200° C., Cr,Si, 
being formed. The properties of this silicide have already 
been described by MM. P. Lebeau and Figueras.—A new 
silicide of manganese described by M. Gin: Paul Lebeau. 
The author gives reasons to suppose that the silicide of 
manganese recently described as new by M. Gin is in 
reality impure SiMn,.—A continuous apparatus for the 
preparation of pure oxygen for use in organic analyses : 
A. Seyewetz and M. Poizat. Acid solution of potassium 
permanganate is allowed to flow into hydrogen peroxide 
solution, The advantages of ease of control and purity of 
the gas are claimed.—The study of a case of isomerism 
in the oxonium combinations of Grignard and Baeyer: W. 
Tschlinzeff. \n attempt to discriminate between the two 
formule suggested by Baeyer and Grignard respectively 
for the addition compounds of magnesium alkyl compounds 
and ether. Thermochemical experiments led to indecisive 
results, but the action of water on the substances obtained 
in different ways tends to support Baeyer’s views.—Methyl- 
ethylketone peroxide: M. Pastureau. Details of the pre- 
paration, properties, and reactions of methylethylketone 
peroxide.—The acyclic unsaturated and f-chlorethyl ketones. 
A method of synthesis of the 4-alkylquinolines: E. E. 
Blaise and M. Maire.—A method of destroying larve in 
plantations of trees: M. Eberhardt. A solution of formol, 
glycerol, and water is used, and details are given of the 
mode of application in different cases. The treatment has 
given excellent results in trees already attacked by larve. 
—A new antelope from the valley of Ituri, Cephalophus 
ituriensts: Maurice de Rothschild and Henri Neuville. 
—The Liriopsida, crustacean isopods, parasites of the 
Rhizocephale : Maurice Caullery.—A precaution to be 
taken in the observation of colours: E. P. Fortin. If a 
coloured object is subject to a constant illumination, the 
colour seems to differ according as the eye is or is not 
exposed to light. The precautions necessary on_ this 
account are indicated in the cases of coloured chemical 
reactions, in meteorological observations, and in the ex- 
amination of paintings.—The Aptian, Gault, and Ceno- 
manian, and on the general characters of the Lower and 
Middle Cretacian in the Atlas of eastern Morocco: W. 
Kilian and Louis Gentil.—The relations between the 
Tertiary strata and volcanic rocks in Anglona (Sardinia) : 
M. Deprat.—The Calabrian earthquake of September 8, 
1905: G. Mercalli. 
New SoutH WALES. 
Linnean Society, November 28, 1906.—Mr. T. Steel, presi- 
dent, in the chair.—Recent travels among the aborigines 
of the north coast of Australia between Broome, on the 
north-west, and the Gulf of Carpentaria, and at Melville 
; Island, for the purpose of ethnological and anthropological 
