1887.] Mr W. Peddie on Transition Resistance. 229 
the value of the product of the specific resistance and the thickness) 
combined with experiments made on the resistance of a very fine 
platinum wire, first, when newly heated, and, secondly, when left 
unheated for some time. The latter experiments would give the 
value of the ratio of the two quantities mentioned. 
Meanwhile, if it may be assumed that the thickness of the con- 
densed gases is of the same order as the thickness of condensed 
moisture and gases on the surface of glass (given by Quincke as 
5(10)~ 5 c.m. — Pogg. Ann. } 1859, and Wied. Ann., 1877), the above 
experiments show that the order of the specific resistance is the 
same as that of ordinary dielectrics. 
Remarks. 
If the film of gas had acted as a perfect dielectric no alteration of 
resistance would have been perceptible. The fact that the resist- 
ance appeared shows that to a great extent, if not entirely, the gas 
assumes the potential of the metal on which it is condensed. Given 
that the gases do assume the potential of the electrodes, it is 
rendered highly probable that the resistance of the film will alter 
with the potential; for the particles of the gas become mutually 
repellent because of their similar electric charge, and so tend to alter 
their relative positions against the attraction of the metal. That 
such change of resistance with potential did occur was evident in the 
experiments I made; for if the initial deflection was obtained after 
the plates were leftunbeated for some hours, and was again obtained 
after they had been connected for a short time to discharge polariza- 
tion, it was smaller in the latter case than in the former, showing 
that the gas had not yet assumed its previous physical condition. 
Again, if the deflections be got as before, and the plates be 
heated and an equal resistance put in circuit (so as to obtain the 
same initial current), and the deflections again be taken, the rate 
of decrease of current with time is always somewhat greater in the 
former case than in the latter. This might be due to alteration 
of resistance with potential, for the potential of the plates increases 
with time after the battery is joined in. On the other hand, it 
might be due to alteration of capacity. 
Note . — In the Plate the point marked 1 corresponds to the first reading of 
the galvanometer for the curves a and c. The point o' is related to the curves 
b in the same way as o is to a and c. 
