308 Mr Willows, On the distance between the striae in the positive 



connected to the terminals of a tube in which a pressure suitable 

 for giving the double striae has been established, then if a spark 

 be passed from a coil, at the instant the initial discharge passes 

 the number of striae in the tube is largely in excess of the 

 number that finally remains. That end of the positive column 

 next to the kathode remains fixed, while the remainder of the 

 striae rapidly move towards the anode and some of them disappear 

 there. While this is taking place the positive column has the 

 appearance of a spiral spring fixed at the end nearest the kathode, 

 compressed from the other end and then suddenly released. This 

 appearance only lasts for an instant, when it has disappeared the 

 column is seen to be doubly striated. If the discharge is main- 

 tained by the battery these double striae generally disappear 

 after a few seconds ; this is brought about by a movement of 

 that component furthest from the kathode in the direction of 

 the anode and so forming a separate striation. The whole are 

 then equally spaced and identical in appearance. In some cases 

 however the doubleness persists, but if the current is considerably 

 increased the change to single striae takes place immediately. 

 If the current is then broken and the discharge restarted the 

 double striae again appear. 



By suitably adjusting the intensity of the current the separate 

 parts of a double stria can be made equally bright and of nearly 

 the same colour ; generally that part nearest the kathode is the 

 brighter and in no case could it be made the weaker of the two. 

 For very small currents the part nearest the anode was generally 

 much the weaker of the two. 



When produced by a coil the most apparent explanation of 

 this double appearance would be to suppose that the coil dis- 

 charges both ways and the separate parts of a double striation 

 are produced by currents in opposite directions. Spottiswoode 1 

 found when his interrupter was changing its note that something 

 like this did actually occur and that the dark parts when the 

 current was passing in one direction became the bright parts 

 when it was passing in the other direction. In such a case, 

 however, the separate discharges can easily be distinguished in 

 a revolving mirror. In the present case whether battery or coil 

 was used examination by a revolving mirror showed that the 

 separate parts were coexistent, so that this explanation will not 

 suffice. 



Further, if the coil was purposely made to discharge both 

 ways the appearance in the tube was totally different from that 

 presented by the double striae. 



Since Crookes (loc. cit.) has shown that a mixture of gases 

 gives rise to different sets of striae, the presence of impurity 



1 Proc. Roy. Soc. Vol. 23, p. 455. 



