Ignition of Gases by Hot Wires, 631 



the pressure is raised toi-several hundred atmospheres it is 

 impossible to ignite the gas by any current short of fusion of 

 the wire *. 



We have then the remarkable result that from pressures 

 of 20 to 600 centimetres of mercury the same current causes 

 ignition. This again points to ignition being a trigger effect. 



12. Absence of Influence of Electric or Magnetic Fields 

 on Hot }\ire Ignition. 



The connexions for obtaining a high-tension alternating 

 ^electrostatic field are shown in fig. 1. A quartz tube with 

 sealed end is threaded through the wire loop. A metal rod 

 fitting inside the tube is one electrode, the other is the 

 ignition wire. Sparks cannot pass but a fie id high enough 

 to produce " corona " or anything short of it is obtained. 

 When the wire is heated to redness by the passage of a 

 current from cells switching on the high-tension voltage 

 cools it instantly to blackness. This is caused by the move- 

 ment of the air ionized by the strong electrostatic field, 

 repelled from and drawn back to the wire with a fanning 

 action sufficient to cool it out. The glow reappears on 

 the approach of a strong magnet. Moving ions are then 

 swept away as soon as formed and the alternating field 

 has no grip upon unelectrified molecules of gas around 

 the wire. 



Differences of one per cent, in the brightness of a wire 

 can be measured. To this degree of sensitiveness the change 

 of brightness is a means of indicating the presence of ions in 

 the gas around it by their fanning action. When the electric 

 field around the wire is unidirectional and insufficient to cause 

 ionization by collision, an alternating magnetic field might 

 by its action on the thermionic discharge have made the 

 latter visible. None could be observed, though the field 

 strength was pushed to a high value. Placing the wire in a 

 tube through which a stream of methane and air was passed, 

 no effect on surface combustion of a steady field of 30,000 

 lines per sq. cm. could be observed. This again points to an 

 extraordinarily intimate relation between the metal and the 

 burning gas. 



13. Application of lie suits. 



Apart from the question of endurance or mode of appli- 

 cation, it is possible by the use of filaments of metals such 



* " Gaseous Combustion at High Pressures," W. A. Bone and others. 

 (Phil. Trans. Roy. Soc. Series A, vol. ccxv. p. 281. 



2X2 



