170 TirE 8TR0CTURE OF THE NUCLEUS. 



1^. Mi^ceUaneom experimeiiU. — The uccurreiice uf an insuliited needle makes 

 this form of electrometer peculiar, and a special lever is needed to put the needle 

 to eai'th at will. If the quadi-ants are charged equally and o{)posite with the 

 capsule earthed, = « V^ V^. Hence the deflection is not zero but of a raaijjnitude 

 varying with F^, the potential of the needle. If the needle is put to earth, = 0, 

 and this may l^e used as a test for symmetry of the quadrants and needle. If V^ 

 is zero, Q will vanish for all values of V^. I omit the data. 



Holes were dift'eiently cut in the vane of the needle, but the effect was always 

 disadvantageous, as might have been expected from theory. 



The highest sensitiveness was obtained with a twisted silk bifilar, each thread 

 single-fibered. The constant obtained was a = .5. Deflections, however, were too 

 prolonged and ci'eeping to make this result of value even if a quartz fiber had 

 been used. 



14. Summary. — With the use of a danqnng capsule in which the air (lanq)er or 

 disc of the needle lies symmetrically in the right section of a cylindrical l)ox, with 

 only just space enough at the edge to secure freedom of motion, not only may 

 complete aperiodicity be secured if desirable, but a charge may effectively be 

 imparted to the needle by induction, which is all but equal to the inducing charge. 

 The voltages to be measured are necessai'ily small. 



In view of the light needle, the absence of liquid contacts, the sensitiveness of 

 the appai'atus may be made upwaids of 10 times greater than is customary where 

 liquid contacts are em[>loyed. An advantage of the instrument is its simplicity, its 

 small capacity, its immediate adaptation to quartz fiber suspension, the attainable 

 stability. For the latter purpose the air within the instrument must be dry, and 

 the difficulty of securing this perfect insulation is an objection to the instrument. 



The sensitiveness may be enoimously incieased, however, by charging the 

 needle by contact and using the capsule merely to retain its high potential. As 

 few as ten storage cells will suflice to effect this charging. It is necessary to 

 provide means for the loss of chai-ge of the needle, and this is done in the next 

 section. 



TRANSMISSION OF THE CHARGE BY IONIZED AIR. 



15. Phospliorus emanation. — The ionizer used for experimental purposes was 

 phosi)horus. It was attached to the inner faces of the metallic bariiers, <-, e, behind 

 discs of wire gauze. Otherwise the method of expeiimeut was the same as above, 

 except that the reversed deflection (recoil), after the permanent deflection had been 

 i-eached, was also lecorded. As the danqiing ratio was 8/1, the arc of recoil from 

 the permanent deflection should be 1/0 of its value. The effect is always larger, 

 after which the zero is asymptotically regained. It follows that a charge succes- 

 sively entere upon and vanishes from the needle through the ionized air. 



The data showed that both the temporaiy and the permanent deflections vary 

 as tlie potential of the needle, but that the recoil increases at an accelerated rate 

 for higher potentials. The sensitiveness varies with the activity of the phosphorus. 

 Again the temporary and the permanent deflections are greatest when the recoil 

 is least. 



