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POPULAR SCIENCE REVIEW. 
projecting from the top of the casing is cemented a metal cap, from which 
project three prongs, so arranged that the wire must be slightly bent in 
passing between them, it being thus prevented from slipping. The insu- 
lator is secured in its place by a pin which projects from the pole into an 
opening in the under side of the glass. Both the cup and casing are 
thus so completely insulated, that there can be no communication between 
the wire and the pole. This apparatus appears from its simplicity to be 
an economical and cheap one. 
Different Spectra produced by the same Element . — From the experiments 
of MM. Pliicker and Hittorf, it has been proved that certain bodies, such 
as nitrogen and sulphur, do not give a unique spectrum, but, according to 
the temperature to which the incandescent vapour is submitted, two very 
distinct spectra. To ascertain this, they passed through the tubes, con- 
taining gas or vapour at a pressure of a few centimetres, first the ordinary 
current of Ruhmkorff’s induction coil, then the same current with its 
calorific action increased by the interposition of a Leyden jar. By varying 
the surface of the jar and thus gradually raising the temperature of the 
gaseous body, they found that the transition from one spectrum to another 
was rapidly accomplished. Hence it would seem that a considerable 
molecular alteration of the body had taken place. When the temperature 
was lowered the distinction disappeared. The first spectrum was com- 
posed of large bands, more or less regular, but oftener presenting the 
appearances of channelled spaces cut by black rays. The second exhibited 
brilliant rays on a more or less luminous ground. For a more detailed 
account of these researches we must refer our readers to the Chemical News , 
No. 229, p. 195. 
Theory of the Candle Flame. — M. Morren, who has been one of the latest 
writers upon this subject, thus sums up his opinion. The theory of the 
candle flame now admitted must be somewhat modified. The base of the 
flame being blue, is the vapour of carbon preserved from combustion, 
but kept at a very high temperature by the envelope of hydrogen, 
the more combustible element of the gaseous carbides from the decom- 
position of wax ; the hydrogen alone uniting with the oxygen of 
the air. Above the blue part comes the luminous part, produced by the 
passage of the carbon from the gaseous to the solid state, giving out in the 
passage a considerable amount of heat. The black cone which surrounds 
the wick of the candle is formed of gaseous carbides of hydrogen, which 
only burn in the upper part of the flame when they come into contact with 
oxygen. Hydrogen, besides being not only very combustible, but very 
subtle, diffusive, and penetrating, its combustion takes place under con- 
ditions in which it would be impossible for other gaseous bodies to burn. 
If a candle be gently moved so that the flame may be inclined, and the 
air allowed to come in contact with the vapour of hydrocarbons which 
surround the wick, we see the hydrogen take fire, and above the flame 
appears the blue vapour of carbon. — Vide Chemical News , No. 224. 
Electric Properties of Gun-cotton. — The late experiments of Professor 
Johnston on the subject of the electro-developing power of gun-cotton, 
have been carried out by Professor Silliman, with similar results in both 
cases. The latter savan states that gun-cotton produces the same excite- 
