Complex sentence: He was able to show that the remaining radiation was composed of a second and third type, one of which was deflected by a magnetic field (as were the familiar "canal rays") and thus identical to Rutherford's beta rays.
Split into simpler sentences: He was able to show that the remaining radiation consisted of a second and third type of rays. One of those was deflected by a magnetic field (as were the familiar "canal rays") and could be identified with Rutherford's beta rays.