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XXXVIII. On the Conducting Power of certain Flames and of 

 Heated Air for Electricity. By Thomas Andrews, M.D.* 



TN some recent memoirs on electricity it has been assumed 

 that the discharge of electricity through flame depends 

 simply upon the temperature to which the air in the flame is 

 elevated. Thus Dr. Ritchie observes that " the flame of a 

 blowpipe is a hollow cone containing highly rarefied air. The 

 electric fluid will therefore glide along such a cone exactly 

 as it does along the interior of a hollow cone of glass partially 

 exhausted of air. We are therefore not to regard flame as 

 a conductor of electricity in the ordinary sense of the term, 

 when the only part it performs in the conduction is that of 

 forming a partial vacuum f." These remarks refer to common 

 electricity ; but Mr. Faraday likewise assumes that the rela- 

 tions of flame and heated air to electricity of low tension are 

 the same, in his excellent paper on the " Identity of Electrici- 

 ties derived from different Sources." In order to prove that 

 the latter variety of electricity may be discharged by heated 

 air in the same manner as the former, he performed the fol- 

 lowing experiment. Having attached fine platina wires to the 

 poles of a galvanic battery of 20 pairs of plates, and brought 

 their extremities very close to each other, but without touch- 

 ing, he found that where they were heated to bright redness 

 by the application of the side of a spirit-lamp flame, the cur- 

 rent was freely transmitted. On putting the ends of the wires 

 very close by the side of and parallel to each other, but not 

 touching, the effects were, perhaps, more readily obtained than 

 before. " These effects," he continues, " not hitherto known 

 or expected under this form, are only cases of the discharge 

 which takes place through air between the charcoal termina- 

 tions of the poles of a powerful (galvanic) battery when they are 

 gradually separated after contact. Here the passage is through 

 heated air, exactly as with common electricity J." 



On the other hand the celebrated experiments of Erman, 

 which were repeated and extended by Biot, are opposed to 

 this simple view of the subject, and tend to prove that in the 

 power of conducting electricity of feeble tension flames pre- 

 sent some remarkable properties which are different in flames 

 of different kinds, and cannot therefore be identical with those 

 of heated air. The experiments of Erman, however, refer 

 only to flames; and as the whole subject was involved in much 

 obscurity, although connected with one of the most remark- 



• Communicated by the Author. 



t Philosophical Transactions for 1828, p. 376. [An abstract of Dr. 



Ritchie's paper was given in Phil. Mag, & Annals, N.S. vol. v. p. 223.- — Edit.] 



X Ibid. 1832, pp. 26, 27. [or Lend, and Edinb. Pkil. Mag., vol. iii. p. 165. j 



