182 Dr. Andrews on the Conducting Power of certain Flames 



property of flame and heated air. That the same current, 

 when moving in opposite directions, will overcome with a dif- 

 ferent degree of facility any obstacle in its path appears, so far 

 as our present knowledge of this subject extends, to be a ge- 

 neral law of electricity. For illustrations of this principle, I 

 may refer to the phaenomena presented by the discharge of 

 electricity of high tension across air ; to the interesting expe- 

 riments of Davy, in which different effects were obtained in 

 the discharge of a }iowerful battery by reversing the termina- 

 tions of its poles; to those of Peltier on the alterations of the 

 temperature of metallic junctions from the passage of feeble 

 voltaic currents ; and, finally, to the observations of Bec(|uerel 

 on the facility with which the positive electricity overcomes an 

 obstacle when the two electricities are separated by the agency 

 of heat in a closed metallic circuit. 



But even assuming the accuracy of this principle, we have 

 still to inquire whether its cause can be discovered in particular 

 cases. The unipolar pro[ierty of the flame of alcohol, which 

 was discovered by Erman, and which Biot has explained with 

 so much precision and accuracy, furnishes an explanation of 

 some of the preceding results, and may, perhaps, be applied 

 to them all. If heated air and the flames of charcoal and al- 

 cohol conduct with more facility the positive than the negative 

 electricity, and if the surface of contact of each pole with the 

 heated air or flame be different, it is evident that the current 

 will find the greatest difficulty in passing when it is the nega- 

 tive pole whose contact is least. This conclusion agrees per- 

 fectly with one of the experiments which have been described 

 on the flame of charcoal. But it is more difficult to apply the 

 same explanation to the other experiments, unless we assume 

 that the contacts of the flame of coal gas with the metallic 

 aperture from which the gas issues, of the flame of charcoal 

 with the ignited charcoal itself, and of the heated air above 

 an Argand lamp with the flame, are more intimate and perfect 

 than can be obtained between the flame or heated air and a 

 platina wire introduced directly into them. It does not appear 

 to be improbable that this is actually the case. 



Although the general conclusions that follow from these 

 experiments agree with those of Erman, yet when they are 

 minutely compared, an apparent discordance will be observed 

 to exist between them. According to Erman, when the poles 

 of a pile charged with a solution of common salt are hitroduced 

 into the flame of alcohol, the divergence of the leaves of elec- 

 troscopes connected with each pole did not sensibly diminish, 

 the flame in this case apparently insulating the current. That 

 the insulation, however, was not perfect the experiments which 



