[ 237 ] 

 XXXVI. Intelligence and Miscellaneous Articles. 



EXPERIMENTS TO SHOW THE EXISTENCE OF A NEW SPECIES OF 

 RESISTANCE TO THE TRANSMISSION OF ELECTRICITY. BY 

 M. J. M, GAUGAIN. 



THE theory of Ohm rests, as is known, on the fundamental idea 

 that the electric movement transmitted by a conducting body 

 is subject to the same laws as the movement of heat in a solid body ; 

 and all the consequences which have been drawn from this hypo- 

 thesis have hitherto been verified by experience. The observations 

 which form the subject of the present notice, seem to establish a 

 new analogy between heat and electricity : just, in fact, as in the 

 case of heat there are two species of conductibility — the one inter- 

 nal, the other external — so it seems necessary to admit two species 

 of electric conductibility, in order to account for the facts I am about 

 to mention. 



I formerly stated that the flow of electricity, of uniform intensity, 

 down a cotton thread in a constant state of tension,varies inversely as 

 the length of the thread. This law is true, not only of cotton thread, 

 but of the greater number of bad conductors, — of gum-lac, for in- 

 stance, and porcelain, and the glass which is used for the isolating 

 supports of electric machines. Hitherto I have found but a single 

 body to which the law in question does not apply, — the glass, namely, 

 which is used in the construction of disengaging tubes. 



I have proved that the resistance of a glass tube of this kind is 

 absolutely independent of its length. This result, which at first 

 sight seems strange, is easily explained on the hypothesis that there 

 are two sorts of electric conductibility — the one internal, which con- 

 sists of the greater or less facility with which electricity passes from 

 point to point of the same body — the other extertial, which consists 

 of the greater or less facility with which electricity passes through 

 the separating surfaces of two different bodies. In the greater num- 

 ber of substances the external conductibility is very great, and the 

 resistance may then be considered as exclusively internal. It is 

 then, as I have said, inversely proportional to the length of the con- 

 ductor ; in the case of tube-glass, on the contrary, the internal 

 conductibility is very great ; the resistance is altogether external, 

 and ought therefore to be — as in fact it is — independent of the 

 length of the conductor. 



The nature of the resistance offered by tube-glass to the passage 

 of electricity may be rendered obvious in a very simple manner : — 

 If one extremity of a tube of this glass be taken in the hand, and 

 with the other an electroscope, previously charged, be touched, the 

 electroscope is almost instantaneously discharged, unless, indeed, 

 the atmosphere be very dry ; but if the tube be divided into eight or 

 ten pieces, fastened together by means of somewhat fine wire, and 

 the electroscope be now discharged by means of this chain — part 

 glass, part metal — it will be found that a considerable time is re- 

 quired for the passage of the electricity. It may be sliown, more- 

 over, that the total resistance of a cliain of the kind I have just 



