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 facility with which a spark passes between electrodes. Elster and Geitel showed that if two electrodes were separated by a distance such that the spark just refused to pass, on bringing near a specimen of radium the spark at once passes. This effect is best shown with short sparks from a small induction coil. The Curies have observed that radium completely enveloped by a lead screen 1 cm. thick produces a similar action. The effect in that case is due to the γ rays alone. This action of the rays can be very simply illustrated by connecting two spark-gaps with the induction coil in parallel. The spark-gap of one circuit is adjusted so that the discharge just refuses to pass across it, but passes by the other. When some radium is brought near the silent spark-gap, the spark at once passes and ceases in the other.

Hemptinne found that the electrodeless discharge in a vacuum tube began at a higher pressure when a strong preparation of radium was brought near the tube. In one experiment the discharge without the rays began at 51 mms. but with the radium rays at 68 mms. The colour of the discharge was also altered.

Himstedt found that the resistance of selenium was diminished by the action of radium rays in the same way as by ordinary light.

F. Henning examined the electrical resistance of a barium chloride solution containing radium of activity 1000, but could observe no appreciable difference between it and a similar pure solution of barium chloride. This experiment shows that the action of the rays from the radium does not produce any appreciable change in the conductivity of the barium solution.

Kohlrausch and Henning have recently made a detailed examination of the conductivity of pure radium bromide solutions, and have obtained results very similar to those for the corresponding barium solutions. Kohlrausch found that the conductivity of water exposed to the radiations from radium increased more rapidly than water which had not been exposed·