It will be noticed that, the value of m/e is considerably greater for Tube 3, where the opening is a small hole, than for Tubes 1 and 2, where the opening is a slit of much greater area. I am of opinion that the values of m/e got from Tubes 1 and 2 are too small, in consequence of the leakage from the inner cylinder to the outer by the gas being rendered a conductor by the passage of the cathode rays.
It will be seen from these tables that the value of m/e is independent of the nature of the gas. Thus, for the first tube the mean for air is .40×10-7, for hydrogen .42×10-7, and for carbonic acid gas .4×10-7; for the second tube the mean for air is .52×10-7, for hydrogen .50×10-7, and for carbonic acid gas .54×10-7.
Experiments were tried with electrodes made of iron instead of aluminium; this altered the appearance of the discharge and the value of v at the some pressure, the values of m/e were, however, the same in the two tubes; the effect produced by different metals on the appearance of the discharge will be described later on.
In all the preceding experiments, the cathode rays were first deflected from the cylinder by a magnet, and it was then found that there was no deflexion either of the electrometer or the galvanometer, so that the deflexions observed were entirely due to the cathode rays; when the glow mentioned previously surrounded the cylinders there was a deflexion of the electrometer even when the cathode rays were deflected from the cylinder.
Before proceeding to discuss the results of these measurements I shall describe another method of measuring the quantities m/e and v of an entirely different kind from the preceding; this method is based upon the deflexion of the cathode rays in an electrostatic field. If we measure the deflexion experienced by the rays when traversing a given length under a uniform electric intensity, and the deflexion of the rays when they traverse a given distance under a uniform magnetic field, we can find the values of m/e and v in the following way:-
Let the space passed over by the rays under a uniform electric intensify F be l, the time taken for the rays to traverse this space is l/v, the velocity in the direction of F is therefore
so that ϑ, the angle through which the rays are deflected when they leave the electric field and enter a region free from electric force, is given by the equation
