176 Scientific Intelligence. — Mechanical Philosophy. 



coke or coal become thoroughly ignited, and even then the conducting 

 power depends less on the heat than on the act of combustion, for 

 when the charcoal was placed in a tube of glass and connected by 

 wires with the opposite piles, it produced no change in the needle 

 though red hot, until the heat of the furnace melted the glass around 

 the charcoal, and then the effect was much less than when the char- 

 coal was exposed to active combustion. 



When three troughs of sixty plates, each, four inches square, were 

 charged with muriatic acid and water connected laterally so that the 

 poles of the same name were together in connection, a cyHnder of 

 charcoal one-eighth of an inch in diameter, being placed in the cir- 

 cuit, the magnetic needle situated over the charcoal did not deviate. 

 But when the troughs were connected so as to form a single battery of 

 one hundred and eighty plates, tlien the needle placed under the char- 

 coal, was strongly divergent, especially when the circuit was, from 

 time to time, interrupted. 



It IS well known, however, that charcoal conducts electricity at 

 common temperatures. The fine experiment of the electric current 

 between charcoal points in a vacuum, shews that combustion is not 

 necessary. But why does not the current commence until the points 

 are in contact, and begin to redden, and why does it continue when 

 they are gradually separated to a considerable distance, an event 

 which does not take place between metallic points ? What is the lu- 

 minous arc between the points, which appeared to conduct electrici- 

 ty ? Is the flame, which is only carbon in the state of vapor, a con- 

 ductor of the galvanic fluid? The experiments of Erman have 

 thrown light on these phenomena, or rather they have shewn tibat 

 there are in the conducting power of flame singular anomalies. 



It is desirable tliat the subject should claim the further attention of 

 able experimenters. G. D. — Bib. Univ. Juin, 1829. 



5. On the Deflection of Light, by M. Halbat. — The phenomena 

 of deflection, the examination of which has lately furnished so ma- 

 ny arguments against the hypothesis of Newton, and in favor of tlie 

 opinion of Descartes, appear to the author not to hav^e been suffi- 

 ciently examined. He accordingly performed a great number of 

 experiments, which proved that the deflection of light is not modified 

 either by the density or chemical nature of the substance ; and hav- 

 ing ascertained this, he turned his attention to the great powers of 

 nature, and having prepared wires and plates of iron, copper and sH- 



