ABSTRACT
Mr. C. G. Darwin began an investigation in the University of Manchester to examine the relation between the velocity of cathode rays and the frequency of X rays excited by them in different radiators. The cathode rays were generated by the electric discharge in a suitable vacuum-tube, and by means of an adjustable magnetic field rays of definite speed were allowed to fall on a radiator. As soon as the Coolidge tube was put on the market, it was recognized that it afforded a much more convenient method of attacking a part of the main problem and over a much wider range of voltage. The energy of the electrons striking the anticathode in the high vacuum of the Coolidge tube depends only on the voltage applied. The current could be controlled by an insulating handle coming through a small opening. The conductors for the heating current passed inside the hollow metal tubes.
