The London, Edinburgh and Dublin philosophical magazine and journal of science . ured accurately, and the radium had to bemoved closer to the leaking system. The final arrangement is shown in fig. 1. One gram ofradium was strewn uniformly over the bottom of a lead boxB, the top of the box was covered with a thin aluminium leafI 00043 mm. thick in two sets of observations, and with analuminium plate 0*083 mm. thick in a third. Above the radium a thick lead plate PP had a hole 2*5 diameter drilled in the centre, this was covered on top * Nachrichten d. K. Gesell. d. Wissen. Gottingen. 190
The London, Edinburgh and Dublin philosophical magazine and journal of science . ured accurately, and the radium had to bemoved closer to the leaking system. The final arrangement is shown in fig. 1. One gram ofradium was strewn uniformly over the bottom of a lead boxB, the top of the box was covered with a thin aluminium leafI 00043 mm. thick in two sets of observations, and with analuminium plate 0*083 mm. thick in a third. Above the radium a thick lead plate PP had a hole 2*5 diameter drilled in the centre, this was covered on top * Nachrichten d. K. Gesell. d. Wissen. Gottingen. 1901. f In these experiments his electrometer was not sufficiently sensitiveco measure the leak due to the corpuscles themselves, so that a lowerlimit only could be found. X This substance is generally spoken of as radium, though it is reallymostly radium chloride! 552 Mr. J. J. E. Durack on the Specific Ionization with a plate of aluminium L 0*083 mm. thick, and made air-tight by screwing down a thicker plate of aluminium over it Fig- 1. 7~o EtECT/roMETef? 7o pump a ? MCL too. and melting an elastic glue into the crevices. A ring of eboniteRR separated the brass box CC from the lead plate. Abovethe plate L and 13*5 mm. from it was placed another platepp\ the back of this plate was of lead, which was turned soas to form a thin rim of lead on the side nearer L; an alu-minium plate similar to L was then placed over the rim andfastened to it so that there was an air-space between thealuminium and the lead ; pp was connected to a quadrantelectrometer with a rod passing through the ebonite plug Eand shielded from electrostatic effects. The space inside CC was in communication with a pumpand McLeod gauge. All joints between metal and ebonite and between metaland glass were made air-tight with sealing-wax. The plate PP was 8 cms. diameter, and the apparatus isdrawn to scale in fig. 1. During the time the observations were being made CC and Bwere kept connected to earth, and PP to one pol
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