TROWBRIDGE. — RONTGEN RAYS. 263 



high voltages which can be obtained by the use of the Plantc machine. 

 A Geissler tube containing hydrogen at 1 mm. pressure was placed be- 

 tween the terminals of the Plante machine together with a spark gap. 

 This tube would give only four half oscillations with ten thousand volts 

 and gave twenty half oscillations with approximately 300,000 volts, 

 the electrical circuits beinij the same in the two cases. 



I next placed the additional spark gap in the flame of a Bunsen 

 burner. It is well known that the spark length can be greatly increased 

 in an atmosphere of heated air. On photographing a spark produced in 

 the same circuit, the resistance appeared to be slightly increased by the 

 heated air; doubling the length of the spark, however, made no change 

 in the resistance that was encountered in the heated medium. The phe- 

 nomenon was very analogous to that observed in the receiver exhausted 

 to 100 cm. It is well known that lightning follows currents of heated 

 air, striking into barn doors from which arise hot air currents from hay, 

 and passing into chimneys from which issue heated air. The striking 

 fact is presented that the medium breaks down more easily when it is 

 heated ; but it offers during the oscillations of the liehtninor somewhat 

 more resistance than cold air. 



I was interested to discover whether heating the air in which the spark 

 in the primary of the Thomson Tesla transformer is produced would 

 have any marked effect on the high tension spark of the secondary of 

 such a transformer. It was immediately evident that such heating of the 

 air was detrimental. The high tension sparks immediately ceased to 

 jump at the extreme sparking distance of the terminals. Following this 

 train of thought, I next placed a spark gap of the primary of the above 

 mentioned transformer between the poles of a powerful magnet, giving a 

 field of certainly ten thousand lines to the centimeter. It is well known 

 that when such a field is excited the primary spark appears to be blown 

 out with a loud report, and a great increase of length of spark is obtained 

 in the secondary of the transformer. Applying the method of estimation 

 of resistance by damping to an additional spark gap which was placed in 

 this magnetic field, I found no difference in resistance offered to the 

 spark, whether the magnetic field was excited or not, or whether the 

 spark jumped across the direction of the magnetic lines or in the same 

 direction. Is it possible that, the ether being already under a mag- 

 netic stress, the addition of a powerful electrostatic stress serves suddenly 

 to break down the ether? It is well known that a blast of air imi- 

 tates the action of a magnetic field, and produces also a great increase of 

 spark in the secondary circuit of a Thomson Tesla transformer. It prob- 



