380 Prussian Blue. 
19. Electric Light.—Having a metallic wire covered 
with silk, form it into a close flat spiral, taking care that 
the revolutions touch each other. Their number may 
be arbitrary—more than twenty-four have not been used. 
The properties of this spiral when it forms part of the 
voltaic circuit are well known, but pass through it a 
charge of common electricity, such as may be taken by 
two square feet of coated surface, moderately charged, 
and a vivid light, somewhat resembling that of an artificial 
fire-work, will occur, originating from the centre of the 
spires, it may be seen very distinctly without darkening 
the chamber where the experiment is made. M. Leopold 
de Nobili, who describes this experiment, considers the 
phenomenon as perfectly new. If the wire be folded 
backwards and forwards, so as to form a rectangular sur- 
face, then the electric discharge only produces a faint 
light at each corner, and this he considers as the light 
produced by the escape of the electricity into the atmos- 
phere; but the light from the spiral is said to be so vivid 
and distinct, that once seen, its dissimilarity from the for- 
mer must be instantly evident. He has therefore called 
it electro-magnetic light, because of its relation to the 
magnetic state of the spiral, thinks that it might be made 
continuous if a sufficiently powerful voltaic battery were 
used, and has bui little doubt that the aurora borealis is 
such a light, elicited by the magnetic state of the earth. — 
20. White Copper.—According to M. Keferstein, a metallic 
composition resembling silver has been employed under the 
name of white copper, for a long time, at Suhl, in orna- 
menting fire-arms. M. Brandes, by analysis, found it to be 
an alloy of copper and nickel. M. M. Keferstein and Mul- 
ler have recently sought out the origin of this substance, 
and have ascertained that it is found in the scoria of some 
ancient copper works, formerly attached to mines now 
abandoned. ‘The white copper which had formerly been 
rejected as useless, is now obtained by fusion, for the pur- 
_ pose above stated. 
21. Prussian Blue.—Mr. Badnall, of Leek, has taken 
outa patent for improvements in dyeing with Prussian Blue. 
The improvement consists in preparing the Prussian Blue, 
