Excerpt from The American Journal of Science

The experiments which I am about to describe were begun before the appearance of the recent papers by Elster and Geitel and by Allan. And were continued in view of the dis crepancy between their results, and also because indications had been Obtained of results not Observed by either. A fine copper wire P in diameter was suspended horizontally, about 8 meters above the round, between two neighboring build ings; it was attache to the negative pole of a Wimshurst machine, driven by a small motor, the positive pole of the Wimshurst being earthed. A parallel spark-gap 5mm long served to kee the potential-difference constant during an exposure whio was usually continued for three hours. The activity of the wire was observed in a cvlindrieal testing vessel, with the central rod connected to one pair of uadrants of an electrometer: the rod was protected by an eart Ied guard late in the usual manner. The bottom of the testing vesse was easily removable and bore four vertical brass rods 'ust within the walls of the cylinder, and about these rods the exposed wire could be wound. The electrometer was of special con struction, with sulphur insulation and adjustable quadrants; the needle was of silvered paper and the suspension a quartz fiber dipped in a solutibn Of calcium chloride to render it con ducting, as in Dolezalek's electrometer. With the suspension used and 90 volts oii the needle, the sensitiveness was sufficient per volt with the scale at one meter), and the instru ment was very steady. When the potential on the needle was kept constant, the sensitiveness of the apparatus to a small sample of uranium oxide did not vary appreciably over a period of several days. Accidental motions of the needle were largely avoided by enclosing the connecting wire between electro meter and cylinder in an earthed brass box, outside of which a small electromagnet served to insulate or short circuit the quadrants.* The exposed wire could be put into the cvlinder without disturbing the connections or jarring the electrometer, so that readings could be begun nnmediately; the only time lost after the end of the exposure was in taking in the wire and winding it about the frame. After the wire had been put into the testing vessel, measurements of the ionization current were made at intervals of three minutes during the first part of the experiment when the change in activity was rapid; later, readings were taken every six minutes.

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