Cathode Disintegration at Low Pressures. 145 
were magnetized first, so far as is known, some fifty years 
ago, and are not known to have been remagnetized since. 
The magnets 140, 138, and 60 vary in age from five to 
twenty years. They too are supposed never to have been 
remagnetized. It would seem worth inquiry whether mere 
age, as apart from change of strength, may not tend to 
increase the pole-distance. 
_ Experiments with a set of collimator magnets, following 
the same lines as those with the six mirror magnets, would 
have been of fully greater interest ; and the combination of 
the results obtained for the cellimator magnets alone, and 
for the mirror magnets alone, with results obtained by 
employing the collimators to deflect the mirror magnets, 
would have formed a promising though laborious line of 
research. Ordinary magnetometers, however,—except those 
by Messrs. Cooke of the India Office pattern—do not possess 
a deflexion-chamber sufficiently long to take a collimator 
magnet; and no opportunity of carrying out deflexion 
experiments on collimators has presented itself. 
XV. Cathode Disintegration in the Discharge through Gases 
at Low Pressures. By L. Hotporn and L. W. Austin *. 
HE use of the disintegration of the cathode in the vacuum 
discharge for the production of thin metal films was first 
proposed by Plicker f. This proposal was later carried out 
by Wrightt and Kundt§. The first quantitative observations 
were made by Crookes ||, who compared the disintegration of 
a large number of metals by means of arotating switch which 
connected alternately four cathodes in the same exhausted 
tube with an induction-coil. In each of the experiments, 
which lasted several hours, one of the cathodes was gold, 
which was chosen as the standard with which the disintegration 
of the other metals was compared. Metals with a high melting- 
point were used in the form of wire. The more easily melted 
metals, such as tin, cadmium, and lead, were in the form 
of thick rods surrounded by porcelain cups. In the latter 
cases the gold was in similar form. 
* Communicated by the Authors. See Wiss, Abh. d. P. T. Reichs 
anstalt, Band iv. Heft 1, p. 101 (1903). 
+ J. Plucker, Poge. Ann. cv. p. 68 (1858). 
¢ A. W. Wright, Amer. Journ. of Sc. & Arts, (5) xii. p. 49, and xiv. 
p. 169 (1877). 
§ A. Kundt, Wied. Ann. xxvii. p. 59 (1886). 
|| W. Crookes, Proc. Roy. Soe. 1. p. 88 (1891). 
Phil. Mag. 8. 6. Vol. 8. No. 44. Aug. 1904. L 
