In 1886, Eugen Goldstein observed that rays flowing in a direction opposite to that of the cathode rays were positively charged. Such rays were named as canal rays because they passed through the holes or the canals present in the perforated cathode. In 1898, WilhelmWien, a German physicist, measured e/m for canal rays. It was found that the particles constituting the canal rays are much heavier than electrons. Also unlike cathode rays, the nature and the type of these particles varied depending upon the gas present in the cathode ray tube. The canal rays had positive charges which were whole number multiples of the amount of charge present on the electron. The positive nature of the canal rays was explained as follows:
In a cathode ray tube, the electrons emitted from the cathode collide with the atoms of the gas present in the tube and knock out one or more electrons present in them. This leaves behind positive ions which travel towards the cathode. If the cathode has holes in it ,then these positive ions can pass through these holes or canals. Hence, they are called the canal rays. The canal rays are shown in Fig. 3.2.

When the cathode ray tube contained hydrogen gas, the particles of the canal rays obtained were the lightest and their e/m ratio was the highest. Rutherford showed that these particles were identical to the hydrogen ion (hydrogen atom from which one electron has been removed). These particles were named as protons and were shown to be present in all matter.