134 Method of making Ship Lanterns with Mica and Wire. 
that the watch-lights, those of the powder-room, &c. should 
transmit the light through horn, or other substance capable of 
resisting great shocks. This material is at present sufficiently 
plentiful, and is very well manufactured, in France: but as it 
fell short in the magazines at the beginning of the revolution, 
M. Rochon supplied its place for the ship-lanterns by a net- 
work of wire, of a large mesh, covered with a light coat of 
transparent isinglass. This “artificial horn was at that time of 
great service in “the navy. 
The arrival of an American vessel havin g on board several 
pieces of foliated mica perfectly transparent, | sugvested to 
M. Rochon the idea of employing it in the place of glass or horn, 
in Sua to isinglass and copal varnish, This mineral is 
found in abundance in the quarries of granite in the environs of 
Newport i in North America. Hitherto it has been only known 
in the district of Witten, in Siberia, which furnishes it in large 
flakes. The preparation of this mineral, to render it of use as 
a medium for transmitting light, consists in separating it in plates, 
more or less thick, with a double-edged knife. The Siberians, 
says the traveller Gmelin, use these transparent plates as much 
for their windows as for their lanterns. The Russian navy con- 
sumes a great deal of it; all the window-lights of the vessels are 
of this substance, which, independent of its great transparency, 
resists the strong shock of artillery. The surfaces of the flakes 
or plates of this incombustible mineral are about two ells square. 
M. Vauguelin has found in it ten parts of silex, seven of alumine 5 
and the limits of its specific weight are, according to the calcu 
lations of M. Brissot, between 265 and 293. 
We are assured that the Americans use foliated mica for the 
same purposes as the Russians. They employ also demispherical 
masses of glass to reflect the rays of light in such parts of the 
vessels where the blowing of the wind will not allow of lanterns, 
Although we might be able to procure squares of mica suffi- 
ciently transparent, and thick enough to resist the most violent 
blows, the necessity of ceconomizing a substance so rare, and to 
give it the utmost degree of transparency, determined M. Rochon 
to inclose it between two pieces of tinned iron net-work of a large’ 
mesh, The wires of these meshes, which are manufactured in 
a weayer’s Joom, do not intercept a hundredth part of the light. 
By these means he is enabled to make the squares of an unli- 
tnited size with plates that are of unequal sizes. Gum arabic 
serves to conuect them together; and with some very fine cop- 
per wire, well-tempered, a few stitches made with a fine needle 
will fit it firmly in the frame that incloses it. 
One of the light-houses on the coast of Bretagne, at the 
entranee of the Channel, having had its windows broken by an 
accident, 
