. Conduction of electricity through gases and radio-activity; a text-book with experiments . rough a potentiometer of large resistanceand tap off from the potentiometer a known potential sufficientto give a suitable deflection. Since the deflections are propor-tional to the difference of potential between the quadrants thenumber of scale divisions per volt is known. This value istechnically termed the sensitiveness of the instrument. Anyother deflection on the scale can therefore be converted intovolts by direct proportion. The sensitiveness of course dependsupon the potential of the needle an
. Conduction of electricity through gases and radio-activity; a text-book with experiments . rough a potentiometer of large resistanceand tap off from the potentiometer a known potential sufficientto give a suitable deflection. Since the deflections are propor-tional to the difference of potential between the quadrants thenumber of scale divisions per volt is known. This value istechnically termed the sensitiveness of the instrument. Anyother deflection on the scale can therefore be converted intovolts by direct proportion. The sensitiveness of course dependsupon the potential of the needle and the instrument must con-sequently be standardized each time observations are made ifthere is any change of potential of the needle. 18. Connection of Electrometer to Other Apparatus.—Thewires connecting the electrometer to any other apparatus, onwhich experiments are being conducted, must be screened inmetal tubes connected to earth as already described, § 14. Thetypical general arrangement of electrometer, lamp and scale,key, screen, etc., is shown in the diagram, Fig. 12, which is. Fig. 12. 24 APPARATUS AND GENERAL METHODS self explanatory. The apparatus to be tested would be con-nected, by a screened wire passing through the cage, to themercury cup in the key. The metal tube screening this con-necting wire should pass inside the main cage so that no partof the wire is exposed. 19. Determination of Capacity of Electrometer and System.—In making definite calculations from the observations withthe electrometer it is often necessary to know the capacity ofthe electrometer and connections. One method of determin-ing this is by the ordinary method of mixtures. Let C = the capacity of electrometer and system connectedwith it,C1 = the capacity of a known standard condenser. Charge up the electrometer and connections by means of abattery to a potential V and let the deflection of the needle be ddivisions on the scale. Then connect by means of a key (b),Fig. 11, the standard co
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