226 Mr. H. P. Waran on Mechanical 



since the smallest distance measurable by the ultra-micrometer 

 was 4*3 x 10~£ inch. 



It was observed that whilst the heating current was flowing, 

 the note emitted by the telephone changed very smoothly, 

 showing that no discontinuity in expansion could be detected 

 even with an apparatus capable o£ measuring goo millionth 

 of mi inch. 



My grateful thanks are due to Professor Whiddington for 

 suggesting the experiment and allowing me to use his original 

 apparatus, and also for his advice during the work, which was 

 carried out in the University Physics Laboratories. 



Leeds University. 



XXII. An Interesting Case of Mechanical Disintegration caused 

 by Positive Ions. By H. P. Waran, M.A., Government of 

 India Scholar of the University of Madras* . 



WHILE studying the effect of a transverse magnetic 

 field on the spectrum of an electric discharge through 

 a rarefied gas, it occurred to the writer to examine the extent 

 of the disintegration of the walls of the tube caused by the 

 bombardment of ions deflected on to them by the magnetic 

 field. An ordinary Pliicker discharge-tube containing pure 

 nitrogen at a few millimetres pressure was arranged with its 

 capillary between the conical poles of an electromagnet, :i5 

 shown in fig. 1, and excited by the unrectified current from 

 the secondary of an induction coil. 



It is easy to see that under the influence of: the field 

 transverse to the direction of the discharge, the discharge 

 gets split into two streams, as shown in fig. 2, corresponding 

 to the make and break currents which travel in opposite 

 directions. Further, it is also evident that the corresponding- 

 ions in the two streams travel in opposite directions and get 

 deflected to the opposite sides of the tube. 



Ordinarily the current through the tube is about 2 m.a. 

 and the field about 5000 o G.S.. and very little of any locnl 

 disintegration opposite the pole-pieces is noted. But by 

 screwing the break of the coil and increasing the current 

 through the magnet coils it is possible to pass a heavy dis- 

 charge of about 15 m.a. in a field of the order of 10,000 c.G.s. 

 momentarily, thus intensifying the disintegration consider- 

 ably. Under such circumstances, in a few seconds a grey 

 streaky patch developed on either side of the walls of the 

 capillary, indicating a corrosion of the glass under the 

 * Communicated by Prof. A. W. Porter, F.RS. 



