Question

Why only perforated cathode was used by E Goldstein in the discovery of protons?

Answer 1

i think cathode detects the -ve charges.right

Answer 2

when the electrons pass through the gas in the tube they get accelerated and pass through the tube as being a perforated cathode it attracts the electrons where there are perforations electrons pass by but the opaque area captures the electrons hence a perforated cathode is used
hope u understood 
feel free to ask doubts
happy science towards better world good day!