Section III., 1908. [ 111 ] Trans. R. S. C. 



VIII. — On< the Charges gained hy Insulated Metallic Conductors, sur- 

 rounded by other Conductors, and the Relation of these Charges 

 to the Volta Effect. 



By J. K. EoBERTSON^ M.A., 

 University of Toronto. 

 ' (Communicated by Prof. J. C. McLennan, and read May 26, 1908). 



I. Introduction. 



In 1903 McLennan and Burton ^ found that a metal cylinder, either 

 of lead, copper, zinc, tin, or aluminium, placed within, and insulated 

 from an outer earthed one of the same material, gradually acquired a 

 negative charge, the value of which steadily rose to a maximum which 

 varied with the metal. In November, 1907, McKeon ^ published results 

 of experiments made concerning the same effect, which are not altogether 

 in agreement with those observed by McLennan and Burton. He found, 

 in the case of lead and tin receivers, that the charge acquired was 

 positive. Further, while the observations of McLennan and Burton 

 extended only over a period of some hours, his were continued for 

 several days. During such an interval, moreover, he observed very 

 considerable variations in the value of the charge. From his observ- 

 ations he concluded that these changes took place at definite periods 

 of the day, and, in explanation, suggested a connection between them 

 and the diurnal variations in the ionization of atmospheric air, to which 

 attention has been drawn by Campbell and Wood,^ and others. 



In view of the lack of agreement existing between the two sets of 

 observations, the writer undertook to make a closer examination of the 

 effect in order to ascertain, (1) its cause- and (2) its relation to varia- 

 tions in the earth's penetrating radiation, and to the daily changes in the 

 ionization of the atmosphere noted above. 



On making a rather exhaustive set of observations with different 

 metals, it was found that the sign acquired by the insulated cylinder 

 varied largely with the treatment to which the surfaces of the outer 

 and inner cylinders were subjected. For example, it was found pos- 

 sible, with two particular pairs of cylinders, to alter the sign of the 

 charge merely by thoroughly cleaning the surfaces. A summary of the 

 results obtained in a variety of cases is given in Table I, and it will 



^Phil. Ma^., Sept., 1903. 

 == Phys. Review, Nov.. 1907. 

 8 Phil. Mag., Feb., 1907. 



