IGO CATHODE RAYS. 



in a given magnetic field, with a given mean potential difference between 

 the terminals, tlie path of the rays is independent of the nature of the 

 gas. Photographs. Avere taken of the discharge in hydrogen, air, car- 

 bonic acid, methyl iodide, i. e., in gases whose densities range from 

 1 to 70, and yet not only were the i)aths of the most detiected rays the 

 same in all cases, but even the details, such as the distribution of the 

 bright and dark spaces, were the same; in fact, the photographs could 

 hardly be distinguished from one another. It is to be noted that the 

 pressures were not the same ; the pressures were adjusted until the mean 

 liotential difference was the same. When the pressure of the gas is 

 lowered, the jootential difference between the terminals increases, and the 

 deflection of the rays produced by a magnet diminishes, or at any rate 

 the deflection of the rays where the phosphorescence is a maximum 

 diminishes. If an air break is inserted in the circuit an effect of the same 

 kind is jiroduced. In all the photographs of the cathode rays one sees 

 indications of rays which stretch far into the bulb, but which are not 

 deflected at all by a magnet. Though they stretch for some 2 or 3 

 miles, yet in none ot these i^hotographs do they actually reach the glass. 

 In some experiments, however, I placed inside the tube a screen, near 

 to the slit through which the cathode rays came, and found that no 

 appreciable phosphorescence was produced when tbe non deflected 

 rays struck the screen, wliile there was vivid phosphorescence at the 

 places where the deflected rays struck the screen. These non deflected 

 rays do not seem to exhibit any of the characteristics of cathode rays, 

 and it seems i)ossible that tbey are merely jets of uncharged luminous 

 gas shot out through the slit from the neighborhood of the cathode by 

 a kind of explosion when the discharge passes. 



The curves described by the cathode rays in a uniform magnetic field 

 are, very approximately at any rate, circular for a large part of their 

 course. This is the path which would be described if the cathode rays 

 marked the path of negatively electrified i)articles projected with great 

 velocities from the neighborhood of the negative electrode. Indeed, all 

 the effects produced by a magnet on these rays, and some of these are 

 complicated, as, for example, when the rays are curled up into spirals 

 under the action of a magnetic force, are in exact agreement with the 

 cousequences of this view. 



We can, moreover, show by direct experiment that a charge of nega- 

 tive electricity follows the course of the cathode rays. One way in 

 which this has been done is by an experiment due to Perrin, the details 

 of which are shown in the accompanying illustration. In this exper- 

 iment the rays are allowed to pass inside a metallic cylinder through a 

 small hole, and the cylinder, when these rays enter it, gets a negative 

 charge, while if the rays are deflected by a magnet, so as to escape the 

 hole, the cylinder remains without charge. It seems to me that to the 

 experiment in this form it might be objected that, though the experi- 

 ment shows that negatively electrified bodies are projected normally 



