472 Mr. J. M. Kuehne on the Electrostatic 



leave the movable part reasonably free to rotate, so that 

 there was a possibility for the feeble electromagnetic force 

 to manifest itself. The moment of inertia of the suspended 

 rings was roughly 11000 g.cm. 2 , and when the condenser 

 wjis adjusted so that the period was as large as 8-10 seconds, 

 the deflexions could be easily and unmistakably observed. 

 Having balanced the condenser with an E.M.F. of about 

 40 volts impressed on the primary of the potential trans- 

 former (which means a charging E.M.F. of about 800 volts), 

 and then suddenly applying an E.M.F. of about 100 volts to 

 the magnetizing circuit (which would result in an induced 

 E.M.F. of about '44 volt per turn, indicating a maximum 

 magnet flux of about 170,000 lines) the suspended body 

 could be observed by means of telescope and scale to undergo 

 a steady deflexion of some millimetres. Now reversing the 

 connexions of the magnetizing circuit while the charging 

 circuit remained unaltered, thus changing the relative phase 

 of magnetizing and charging E.M.F.'s by 180°, a deflexion 

 in the opposite direction was noted. These deflexions were 

 always and unmistakably observable whenever the charged 

 body was at all delicately poised, and were reversed whenever 

 the connexion of either circuit was reversed. It was also an 

 easy matter to trace out the connexions of the magnetizing coils 

 and the transformer, and thus determine that the deflexions 

 were taking place in the direction demanded by theory for 

 the effect of the changing magnetic field on the charged 

 body, and opposite to that which would be due to the static 

 magnetic field acting on the charging current. The purely 

 magnetic effect (i. e. the effect due to unsymmetrical magnetic 

 properties of the suspended body), was always very small, 

 and since it is completely eliminated by the method of 

 observation adopted, no further attention was paid to it. 



The angular magnitude of the deflexions was of course 

 dependent upon the restoring couple, and this was due chiefly 

 to the electrostatic attraction between the imperfectly sym- 

 metrical charged bodies. By adjusting the torsion-heads, 

 which were capable of universal adjustment, lateral as well 

 as rotational, and by shifting the stationary part of the con- 

 denser, the sensitiveness was on a few occasions increased so 

 far as to admit of deflexions of from 6-10 cm. on the scale. 

 But this condition would never continue long, and further- 

 more the zero was then so unsteady that reliable quantitative 

 measurements could not be made under the circumstances. 

 The most consistent readings for quantitative work were 

 obtained when the sensitiveness was such as to give a 

 difference in scale readings of *5 to. 2 cm. when the magne- 

 tizing current was reversed. 



