Which subatomic particle was discovered by Goldstein?

Hint: We should first know who Goldstein was. Later, we will look into which field he used to work. Once we understand that then we will find out about the subatomic particle he discovered and we will explain that subatomic particle. In the end we will also know some facts about that particle and its contribution to modern science.

Complete answer:
Step1: Goldstein was a German physicist. He worked on the electrical phenomena In gases. Not only he discovered a subatomic particle but he also discovered the canal rays and anode rays. His experiments were largely based on cathode rays.
Step2: The sub atomic particle he discovered is called a proton. In $1986$, Goldstein used perforated rays, in which he discovered the existence of the positively charged rays in the discharged tube. These rays are first named as canal rays. Later on Rutherford confirmed that there is a positive charge at the center of the atom.
Step3: Proton is a subatomic particle with positive charge equal to that of an electron. It resides at the center of the atom inside the nucleus. The nucleus of a Hydrogen atom or an ${H^ + }$ ion is an example of a free proton.

Note: Most of the mass of the atom is constituted of the proton. A proton is $2000$ times heavier than an electron. In an element the number protons are always the same. Atomic number of an atom is equal to the protons present in the atom. It is very tough for a proton to escape the nucleus of an atom.