Positive rays (or) Canal rays
While conducting experiments on the gas discharge, in 1886, German Physicist, E.Goldstein, discovered that if the cathode used is perforated, luminous streams appe ared in the tube behind the cathode. These streams were called as canal rays. The discharge tube designed by Goldstein is shown in Fig. The tube contains an anode (A), a perforated cathode (K) and a fluorescent screen (S). At a pressure of about 1mm of mercury, a luminous stream of particles were observed behind the cathode proceeding in a direction opposite to that of the cathode rays. Goldstein, called them as canal rays, since they pass through and emerge from the holes, in the cathode in straight lines, opposite to the direction of the cathode rays. From the nature of the deflection produced, by a magnetic field or electric field, these rays were found to be positively charged particles. Hence, canal rays are most commonly known as positive rays.
Properties of Canal rays
i. They are the streams of positive ions of the gas enclosed in the discharge tube. The mass of each ion is nearly equal to the mass of the atom.
ii. They are deflected by electric and magnetic fields. Their deflection is opposite to that of cathode rays.
iii. They travel in straight lines.
iv. The velocity of canal rays is much smaller than the velocity of cathode rays.
v. They affect photographic plates.
vi. These rays can produce fluorescence.
vii. They ionize the gas through which they pass.