The bare fact that cathode rays lose velocity on passing through matter has been known for some time. Leithauser, who discovered that the loss of speed was much greater for slow than for fast rays, made no attempt to discover a law of transmission. It is interesting to notice that the parallel effect in the case of β -rays is so small that for some time it defied detection; its existence, however, has now been definitely proved, and quite recently has been investigated by W. Wilson in as careful and detailed a way as at present seems possible. Wilson found that owing to the limitations of his apparatus he was unable to take measurements accurate enough to distinguish between relations of the type v 0 4 — v x 4 = ax (1) and v 0 2 — v x 2 = ax , (2) where v 0 is the velocity of the rays incident on an absorbent sheet of thickness x, v x is the greatest velocity possessed by the transmitted rays, and a is some constant depending on the absorbing material. Since in these experiments with β -rays the initial velocities ( v 0 ) only ranged between 2·85 and 2·48 × 10 10 cm. /sec., it is, perhaps, hardly surprising that the results should be difficult of exact interpretation. In the case of cathode rays it is easy to produce rays comprised in a wide range, since the difficulties presenting themselves are mainly ones of manipulation, which can usually be surmounted.

The transmission of cathode rays through matter. (1912). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 86(588), 360–370.