II. On repulsion resulting from radiation. Part V

Abstract

This paper commences with an experimental investigation of the amount of repulsion produced by radiation on disks of various kinds, and coated with different substances. The torsion apparatus for this purpose consists of a straw beam, suspended by a fine glass torsion fibre. At one end of the beam is a rod hanging downwards, and capable of taking six experimental disks in a vertical row. The other end of the beam is furnished with a pan and adjustible weights, to balance the varying weights of the disks submitted to radiation. A standard candle, at a fixed distance from the disks, supplies the radiation, and the amount of movement under its influence is measured by a ray of light reflected from a mirror on the beam to a graduated scale. An appropriate arrangement of screens enables any selected disk to be experimented on without the others being affected, and a standard lampblacked disk being always present, the results are capable of intercomparison. The beam, torsion fibre, disks &c., are sealed up in glass, and the whole apparatus is attached to a mercury pump, capable of carrying the exhaustion to any desired point. The experimental powders are mostly chemical precipitates, laid on the surface of mica or pith disks as a water paint, no cement being used to promote adhesion. In other cases the substances are punched, cut, or filed into the shape of disks, 17·25 millims. in diameter.