[ROBERTSON] INSULATED METALLIC CONDUCTORS. US 



in this latter investigation at any rate, secondary radiation is a very 

 important factor in modifying results, arising from the Volta effect. 



II. Experiments — Metal Effect. 



In carrying out the investigation, an attempt was made to examine 

 as many combinations of cylinders as possible, and use was made of the 

 following materials, (1) four outer and two inner cylinders of lead. 

 These were made of lead selected at random from different sheets taken 

 from the stock in the laboratory workshop; (2) two outer and two inner 

 cnes of tin — all made out of the same sheet of the substance; (3) an 

 outer and an inner of zinc, made from two entirely different sheets of 

 the metal. 



An effort was also made to ascertain, if possible, the connection 

 between the surface condition of the metals, and the sign and nature 

 of the charge gained by the inner cylinder. To accomplish this, cylin- 

 ders were washed with the different solutions and abraded to a greater 

 or less extent with emery paper. Sets of observations were also taken 

 with cylinders coated with aluminium and with bronze paints. 



The outer cylinders were about 60 cm. long, and 25 cm. in diameter, 

 the inner ones two or three centimetres shorter, and about 15 cm. in 

 diameter. Larger ones were made in one or two cases, by joining two 

 outer ones and two inner ones together, so as to ascertain in this way 

 the effect of thus varying the size of the cylinders. 



Method of Expertmenting. 



The method of measuring the charge was essentially the same as 

 that employed by the previous investigators. The inner cylinder was 

 insulated from the outer by means of paraffin blocks, and the charge 

 acquired measured by a sensitive quadrant electrometer. Connection 

 was made as shown in Fig. 2. The lid at one end of the outer cylinder 

 had a cylindrical projection of the same material, which was inserted 

 into a box lined with tin foil. This box contained the special arrange- 

 ment devised by Prof. McLennan,^ for malting and breaking the earth 

 conneciiion of one pair of quadrants without altering the capacity of 

 the system. To one end of the inner cylinder was soldered a piece of 

 metal of the same material, which also projected into the box, and was 

 joined to the " make and break." The inner cylinder and all wires 

 connecting it to the electrometer were screened from electrostatic dis- 

 turbances by means of earthed conductors. 



* Phys. Review, March, 1905. 



