AT KEW OBSERVATOEY, 1898 TO 1912. 135 



Time was not available for elaborate experiments, and suspicions were considerably 

 allayed by the fact that the values obtained for the potential gradient were fully higher 

 than the average of those obtained elsewhere. 



3. It was always hoped that an opportunity would present itself for a fuller 

 investigation, but this did not arise until 1909, when Mr. J. S. DINES was attached 

 for a time to the Observatory as student assistant. A number of experiments were 

 made by Mr. DINES. ' A horizontal bamboo rod, carried in a groove made in a paraffin 

 block, was supported on a small platform, attached to the top of a vertical rod. The 

 vertical rod could slide up and down inside a hollow tube, supported by three tripod 

 legs. The height of the bamboo could be altered by sliding the vertical rod or by 

 altering the stretch of the tripod legs, and the distance to which it projected from the 

 centre of the tripod could be altered by moving it in the groove of the paraffin block. 

 A fine horizontal brass tube fixed to the thinner end of the bamboo held the fuse, and 

 a fine wire passed from the brass tube to a terminal on the thicker end of the bamboo, 

 from which another fine wire led to the portable electrometer, which was supported 

 some yards away on a stand of its own. A second essentially identical apparatus was 

 constructed, and simultaneous observations were made with the fuses of the two at 

 the same level, but projecting to different distances from their respective paraffin 

 blocks. Experiments were also made on the distance the one apparatus had to be 

 from the other to be without sensible effect on it. In another set of experiments the 

 fuse holder was carried by a horizontal wire stretched between insulated supports, 

 borne on vertical poles, a considerable distance apart a method employed by 

 Mr. C. T. R. WILSON. The potentials obtained in this way and those obtained 

 immediately before and after at the same spot with the bamboo apparatus, when the 

 bamboo projected to the extent finally approved, agreed so closely that one could not 

 say which was the higher. As between the two methods, it thus appeared wholly a 

 question of greater or less convenience. It was found desirable that smoke from the 

 fuse should be blown quite clear of all the apparatus. This was easily secured with 

 the bamboo apparatus, as the mounting enabled it to be readily swivelled round. It 

 might also have been secured with the other apparatus by having two wires stretched 

 in rectangular directions, and using one or the other according to the wind direction. 

 This promised, however, to be somewhat of a complication, accordingly the principle 

 embodied in the bamboo apparatus was adopted. 



The new apparatus which was then constructed, and which is still in use, resembles the 

 experimental apparatus in having a vertical rod sliding in a tube, but the latter is 

 sunk to some depth and rigidly fixed in the ground. The sliding rod has towards its 

 upper end an enclosing short hollow tube, which projects to an extent depending on 

 the adjustment of a clamp. This outer tube carries a small platform on which is fixed 

 araffin block, serving at once to support and insulate a horizontal bamboo rod. 

 The bamboo has the fuse holder at one end, and at the other a terminal connected by 

 fine wires with the fuse holder and with a portable electrometer at some distance. A 



