SCIENCE ON THE CONTINENT. 
407 
After it is dry, the plate should be warmed again, in order to drive off a 
little of the benzoic acid. By these means, he says that he has been able 
to preserve the colours for three or four days, in an apartment fully exposed 
to a July sun. 
That part of the memoir which relates to the different effects of the 
so-called primitive and binary colours is highly important. It declares all 
secondary colours to be decomposed in the process of Heliochromy ; and in 
order to show the effect of light on a mixed, colour, he selects green as 
affording the most remarkable instance. If, he says, the green be natural, 
such as that of the emerald, of arsenite of copper, of oxide of chromium, of 
sulphate of nickel, of green carbonate of copper, it will be reproduced on 
the helioehromic plate ; but if it be a mixed green, formed, for instance, of 
chrome yellow and Prussian blue, that of a fabric dyed with a similarly 
mixed colour, or of glass coloured by means of yellow and blue pigments 
mixed, then the product by the helioehromic process is invariably blue, 
whether produced by direct action or in the camera. Again, a light blue- 
coloured and a light yellow glass placed together produce a fine transparent 
green ; but whatever be the period of exposure, and however the glasses 
are placed, whether the blue be above or below, or even if it be imprisoned 
between two yellow glasses, the result is invariably not green, but blue. 
In like manner, a red and yellow glass placed together, produce an 
orange colour when held up to the light ; but they uniformly give red 
only to the helioehromic plate : a red and blue glass in combination pro- 
duce at first a violet colour on the plate, which is of itself red, but it soon 
changes to blue. Paper coloured green by means of the leaves of trees, or 
by the vert de vessie, French “ Chinese green” (extracted from the buck- 
thorn), acts very slowly upon the plate, but eventually produces a greyish- 
blue tint, and the same occurs on attempting to reproduce natural foliage 
of a grass-green colour by means of the camera. But if the leaves are of 
a bluish-green tint, such, for example, as those of the dahlia, the blue 
produced on the plate is more decided ; whereas, dead leaves, of a yellow' or 
red colour, produce on the plate yellow or red, more or less pure, according 
to the absence of the blue matter which has been shown to give the green 
colour to foliage. The eye in the feather of the peacock’s tail is well repro- 
duced on the plate in the camera, the colour varying between blue and 
green, according to the angle of incidence at which the light is allow’ed to 
fall on the plate. This report seems to hold forth a fair promise, that 
should Heliochromy fail in its direct intention, it may afford valuable aid 
in the important inquiry into the composition of the solar spectrum, and 
in the evolution of a true theory of colours. 
Bonelli’s Printing Telegraph. — A governmental inquiry is now 
being made into this invention, which is in operation in England, and is 
said to be capable of printing 500 despatches of twenty-five words each 
per hour, an achievement which, it is admitted, would require, under the 
system in use here, twenty wires and fifty clerks ; if the trials give a satis- 
factory result, it is said that M. Bonelli’s arrangement will be at once 
adopted on the Paris, Lyons, and Marseilles line of railway. 
Non-Arsenical Green Pigment. — The Chemisch-technische Mittheil- 
ungen contains an account of a new green colour. Dr. Eisner having 
