1909] 



on Electrical Striations. 



579 



Many changes were made in the way in which the wires used as 

 detectors were arranged ; thus, to prevent any screening of the one 

 wire by the other, an apparatus was used in which the two platinum 

 wires were brought in from opposite sides of the tube, so that there 

 should be no overlapping ; exactly the same results were obtained 

 with this apparatus as with the other. 

 Again, another arrangement, similar 

 to one previously used by Professor 

 H. A. Wilson, was tried, in which the 

 exploring electrodes were kept fixed, 

 and the anode and cathode kept at 

 fixed distance apart were, by means 

 of a float, moved relatively to the 

 exploring electrodes ah, so that these 

 could occupy all positions from the 

 anode to the cathode. The arrange- 

 ment is rer,reseiited in Fig. 3. The 

 exploring electrodes in some of 

 the experiments protruded about a 

 millimetre beyond the ends of the 

 glass tubes into which they were 

 sealed ; in other experiments very 

 fine hollow glass tubes were used 

 to cover the wires, and the wires 

 instead of protruding beyond the 

 glass stopped short at about a milli- 

 metre from the end of the tube ; 

 this arrangement was adopted with 

 the idea of protecting the wires 

 against streams of corpuscles coming 

 down the tube : these by giving up 

 their charges to the wire might cause 

 this to acquire potentials different 

 from those of the gas at the tips of 

 the wire. The results obtained with 

 all these modifications were exactly 

 the same as those obtained with the 

 first type of apparatus, i.e. there was 

 always when the pressure of the gas Fig. 3. 



was low a negative electric force just 



in front, i.e. on the cathode side of the bright part of a striation ; 

 this changed to a large positive force as soon as the bright boundary 

 of the striation was passed ; at a short distance from the front of the 

 striation this force began to diminish and went on diminishing until 

 the front of the next striation. on the anode side was reached. 



Though the indications of all these wire explorers agreed in point- 

 ing to the existence of a negative force in front of these striations, 



