When careful experiments were carried out using perforated cathode in the discharge tube, a new type of rays known as anode rays were revealed. These rays after emitted by anode pass through the pores made in the cathode surface. These rays carry a positive charge and hence also known as positive rays. These rays carry positive charged particles and their e/m ratio changes from gas to gas unlike the e/m ratio of the constituent particles of cathode rays. Actually these positively charged constituents of the anode rays are nothing but the atoms of the gas left after one or more electrons are knocked out of them.
Hydrogen is the lightest element and gives smallest positive particles and is known as proton. The charge carried by a single proton/electron is the smallest charge carried by any particle. For the same reason only, the charge on one proton is called unit positive charge and on one electron is called unit negative charge.