The London, Edinburgh and Dublin philosophical magazine and journal of science . trument is described by Dolezalek* in a recent paper, andwas constructed by Herr Bartels o£ Grottingen. It was ofthe usual quadrant type, but was provided with a verylight needle suspended by a fine quartz fibre. When theneedle was charged to 200 volts it gave a deflexion corre-sponding to 1500 mins., with the telescope and scale at adistance o£ about 150 cms , for 1 volt between the the special purpose for which it was employed, it wasfound necessary to improve the insulation of the quadrantsand to
The London, Edinburgh and Dublin philosophical magazine and journal of science . trument is described by Dolezalek* in a recent paper, andwas constructed by Herr Bartels o£ Grottingen. It was ofthe usual quadrant type, but was provided with a verylight needle suspended by a fine quartz fibre. When theneedle was charged to 200 volts it gave a deflexion corre-sponding to 1500 mins., with the telescope and scale at adistance o£ about 150 cms , for 1 volt between the the special purpose for which it was employed, it wasfound necessary to improve the insulation of the quadrantsand to alter the quadrant connexions. The instrument waseasy to work and gave accurate results. It has been employedrecently by one of us f to measure the small spontaneousionization produced in the air, which has been shown by theexperiments of Elster and Geitel J and C. T. R. Wilson §who used specially designed electroscopes for that purpose. In the experiments on the action of a magnetic field onuranium radiation (fig. 1) a thick layer of uranium oxide was Fig. 1. &*r/>. *fr OyM*. placed on the bottom of a rectangular lead box 5*7 cms. long,1*8 cm. wide, and 4*0 cms. deep, which was placed betweenthe flat pole-pieces of a large electromagnet. The rays, afterpassing out of the lead box, passed between two parallelinsulated plates A and B. One of these plates A was chargedto a of 50 volts above the earth by means of a other plate B was connected to one pair of quadrants ofan electrometer in the usual manner. * Verh. d. D. Physik. Ges. iii. (1901). f Rutherford and Allen, Phys. Zeit. No. 11, 1902. % Phys. Zeit. Nov. 24, 1900. § Proc. Roy. Soc. March, 1901. B2 4 Prof. Rutherford and Miss Brooks : Comparison of Electrostatic disturbances were completely eliminated bycovering the electromagnet and wires leading to it with tinfoilconnected to earth. There was always a small current observed between theplates on account of the spontaneous ionization of the air inthe
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