Projection of Imitation Spinthariscope Appearance

Abstract

WITH reference to Sir Oliver Lodge's letter in NATURE of last week (p. 247), might I venture to say that I exhibited to a large audience the nature of the effect seen in a spinthariscope in a lecture which I gave on radio-activity at the Cavendish Laboratory last term? My plan is somewhat similar to that suggested by one of Sir Oliver Lodge's sons, and consists of two black discs rotating in opposite directions in a mechanical slide. The discs have a large number of transparent spots, so that whenever two of these coincide a flash is produced on the screen. The resultant effect is the same as that seen in the spinthariscope. The coincidences can be arranged so as to be most numerous near the centre.