12 



Miss Martin, Expansion produced [Nov. 11, 



having an area of 264 sq. cm. and 136 sq. cm. respectively. Be- 

 tween the two coatings there was — making allowance for the 

 thickness of the tube walls — a space of 6 — 7 mm. Attached to 

 the outer tube was a gauge to mark the variations of pressure 

 in the gas under observation. 



Having tried various modifications of Meissner's apparatus with 

 no very satisfactory results, it seemed advisable to have his appa- 

 ratus exactly copied — which was easily done as he gives very 

 clear and careful measurements and descriptions. This was 

 accordingly done, the only difference being that instead of the 

 gauge used by Meissner a horizontal tube provided with a small 

 quantity of sulphuric acid was used. 



Observations with this led to the belief that, very frequently 

 at all events, the movement of the acid in the gauge was accom- 

 panied by a luminous discharge through the tube due to induction. 

 Before it could be ascertained if this was invariably the case the 

 outer tube was accidentally broken and it seemed advisable to 

 have the new one made of rather different dimensions. Accord- 

 ingly a piece of tubing about 40 cm. long and having an outside 



diameter of 33 cm. was used for the outer tube whilst the same 

 tube as before (57 cm. long, outside diameter 12 cm.) was again 

 used for the inside. Instead of sealing up the lower end of the 

 outer tube as before, this was now bent and drawn out to serve as 

 a gauge and provided with a tap to cut off the acid from the 



