On one end of the tube was the cathode, which emitted cathode rays. The rays could pass through two metal slits – the first slits act as the anode while the second slit was connected to the earth. The two parallel aluminium plates were connected in an electrical circuit. Closing the circuit would create an electric field between the plates, used to be bend the cathode rays. On the other end of the tube was a large glass sphere. Cathode rays that hit the sphere would create a fluorescent patch. Thomson pasted a scale on the surface of the sphere to measure the deflection of the cathode rays.