Mr. Norman Campbell on Delta Rays. 301 



paragraph 3 is inadequate, and that the variation o£ the 

 current between the electrodes with the potential difference 

 between them is not determined primarily by the speed of 

 the delta rays. Indeed it seems doubtful whether my own 

 experiments or those of any other author in the same direc- 

 tion give any information, even as regards order of magnitude, 

 as to the speed of these rays. The negative conclusions (1), 

 (2), (4), (5), of the Summary are unaffected, but the evidence 

 for (3) and (G) is completely destroyed. The account of the 

 new experiments will be published as soon as possible : it 

 has not been thought desirable to withdraw the present 

 paper from publication, because, in order to arrive at the 

 newer views, an account of the investigations already per- 

 formed and the theory on which they are based is necessary. 



Appendix. 



The high resistances which have been used in these ex- 

 periments for obtaining the compensating current appear to 

 have uses for many physical experiments. Their properties 

 have not been investigated exhaustively, only those important 

 for the purpose in hand being tried. But the results obtained 

 appear worthy of record. The resistances were originally 

 prepared for quite different work*. 



The resistances consist of mixtures of xylol and absolute 

 alcohol contained in glass tubes. The tubes are of thermo- 

 meter bore 13 cm. long, and have bulbs blown at each end 

 into which are sealed platinum wires. The glass round the 

 wires is covered with sealing-wax for better insulation. The 

 tubes are filled by suction and then sealed. They are held 

 in an earthed metal clip which prevents conduction along 

 the surface of the glass. The liquids used ranged from 

 1 part of alcohol to 8 of xylol to 1 part of alcohol to 

 3 of xylol ; the resistances ranged from 4 x 10 11 ohms to 

 7 X 10 9 ohms. The resistance used in this work measured 

 2'3 x 10 11 ohms. The materials used were the ordinary 

 commercial articles dried by lime. 



Bronson, in the paper describing the ionized air resistances 

 usually known by his name, stated that he had tried liouid 

 resistances, but had abandoned them owing to the difficulty 

 of avoiding polarization effects. His choice of liquids must 

 have been unfortunate, for the combination mentioned (which 

 is almost the only one which has been tried) shows no such 



* Campbell, Proc. Camb. Phil, Soc. xv. p 322 (19C9). 



