. Radioactive transformations . meter. A very convenient anduseful type of electrometer for radioactive and other work hasbeen designed by The general construction of theinstrument is seen in Fig. 7. The four quadrants are mounted on amber or sulphur sup-ports. A very light needle, N, is made out of silvered paperand is suspended by a fine quartz fibre or phosphor-bronze needle is charged to a potential of 100 to 300 volts. Ifa quartz suspension is used, this is done by lightly touching themetallic support of the needle with a wire connected with the 1 Dolezalek: Instrume
. Radioactive transformations . meter. A very convenient anduseful type of electrometer for radioactive and other work hasbeen designed by The general construction of theinstrument is seen in Fig. 7. The four quadrants are mounted on amber or sulphur sup-ports. A very light needle, N, is made out of silvered paperand is suspended by a fine quartz fibre or phosphor-bronze needle is charged to a potential of 100 to 300 volts. Ifa quartz suspension is used, this is done by lightly touching themetallic support of the needle with a wire connected with the 1 Dolezalek: Instrumentenkunde, p. 345, 1901. 11ISTORIOAL INTRODUCTION 31 source of potential. It is often more convenient to use a finephosphor-bronze suspension. The needle may then he directlyconnected with one terminal of a battery the other pole of whichis earthed, and its potential kept constant. By the use of a finequartz suspension, the sensibility of the instrument, i. e., thenumber of millimetre divisions, passed over by the spot of light. Fig. electrometer. on the scale for an application of a difference in potential of onevolt between the quadrants, may be made very great. A sen-sibility of 10,000 millimetre divisions per volt is not , however, a very small current is to be measured, it isnot advisable to work with a sensibility greater than 1000 divi-sions per volt, and 200 divisions is often sufficient. 32 RADIOACTIVE TRANSFORMATIONS The quadrant electrometer is essentially an instrument formeasuring the potential of the conductor with which it isconnected, but is indirectly used in radioactivity to measureionization currents. The capacity of the electrometer and itsconnections remains sensibly constant with the movement ofthe needle, and the rate at which the spot of light moves overthe scale is a measure of the rate of rise of potential of the elec-trometer system. This serves as a measure of the ionizationcurrent between the electrodes of the testing vess
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