PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 641 



fication of its points, he concludes, while inclining to the opinion of Cavello, 

 as a general explanation, " that the theory of the fly requires a different 

 expression for an aerial as compared with a liquid diclectio, its behavior is 

 also different in air of different densities; and also when wholly and par- 

 tially inclosed; also, when the points are covered; and even then there is a 

 difference in action, in the presence of flame," from which we infer that its 

 behavior is so modified by circumstances that no one expression represents 

 the law governing its action. 



The Chairman remarked that he had witnessed lately experiments similar 

 to some of those described by Tomlinson, of which more would be said 

 hereafter. The electric disturbance is very beautifully illustrated by the 

 down of the milkweed. If the hand be held at the distance of three feet 

 from the conductor, while the electric machine is in motion, the down darts 

 rapidly between the t^vo. It does not always move in a right line, but 

 approaches the fingers in a curvilinear direction, thus showing the portions 

 of the intermediate air affected. 



Magnesium Light. 



Prof. Eoscoe states that the burning of a magnesium wire, having a thick- 

 ness of 0.297 of a millimeter, evolves a light equal to that of seventy-four 

 stearin candles of six to the pound. If this light lasted one minute, 0.98t 

 of a meter of wire, weighing 0.1204 grm.. would be burned. In order to 

 produce a light equal to seventy-four candles for ten hours, where about 

 twenty pounds of stearin is consumed, 72.2 grms. of magnesium would be 

 required. This light has been used in England for photographic purposes. 



The Spectrum of Carbon. 



Coal, charcoal and the diamond cannot be vaporised by heat when iso- 

 lated, yet M. Morrin, of Versailles, finding the same spectrum produced 

 by the common gas flame, cyanogen, carbonic oxide, carbonic acid, ascety- 

 lene, and the hydro-carbons generally, he concludes this result must be due 

 to the only element common to all these compounds, carbon, and in a state 

 of vapor It follows that the theory of the candle flame must be somewhat 

 modified. The base of the flame being blue, is the vapor of carbon pre- 

 served from combustion, but kept at a very high temperature by the enve- 

 lope of hydrogen, the more combustible element of the gaseous carbides 

 from the decomposition 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 surrounding the 

 wick of the candle is formed of gaseous carburets of hydrogen, which only 

 burn in the upper part of the flame, where they come in contact with oxy- 

 gen. Hydrogen not being very combustible but very subtle, diffusive and 

 penetrating, its combustion takes place under conditions in which it would 

 be impossible for other gaseous bodies or vapors to burn. If a candle be 

 gently moved so th^t the flame may be inclined and the air allowed to come 

 in contact with the vapor of the hydro-carbons which surround the wick, 

 we see the hydrogen take fire, and above the flame appears the blue vapor 

 of the carbon. The latter can only exist alone, and gives its numerous re- 

 [Am. Inst.J P* 



