22 Messrs. W. Spottiswoode and S. F. Moulton. [May 8, 



Holtz machine with a suitable air-spark between the machine and 

 the tnbe, and a small coil with a rapid break. 



If a conductor be made to approach a tube conveying a sensitive 

 discharge, dne to an air- spark in the positive branch of the circuit, 

 a series of effects is produced, of which the feeblest and the 

 strongest are the most pronounced. The transition from one to 

 the other is so rapid that the intermediate phases may be easily over- 

 looked. In the first case, the luminous column is repelled by the con- 

 ductor ; in the second it is broken into two parts which stretch out in 

 two tongues towards the point on the tube nearest the conductor, 

 while a negative halo appears between them. 



That these effects are due to the inductive action of the conductor, 

 or more particularly to re- distributions of electricity in it, co-periodic 

 with the air-spark, and not to any permanent charge, is shown by the 

 following experiments. A non-conductor, whether charged or not, is 

 without effect. The effect of a conductor increases with its size or 

 capacity, and with its proximity to the tube, until the fullest effect 

 (viz., that given by an earth connexion) is produced. That the effects 

 are not due to electro- dynamic, or to magnetic action, is shown by the 

 fact that a coil of wire produces the same result, whether the ends be 

 joined or not. The effects of an iron core and helix with open ends 

 are often comparable with, and sometimes equal to, those when the ends, 

 being connected with a battery, the whole becomes an electro-magnet. 

 The effect upon the interior is, in fact, due to the relief given by 

 the conductor to the electric tension on the outer surface of the tube 

 and the space around it, caused by the individual discharges. 



Instead, however, of connecting a point on the tube with a large 

 conductor or with earth, we may connect it with one or other ter- 

 minal of the tube. And a further study of the subject shows that all 

 the phenomena due to action from without may be produced by means 

 of one or other of these connexions. Connexion with the non-air- 

 spark terminal gives the relief effects described above ; connexion with 

 the air-spark terminal gives another set of effects. Of these the 

 feeblest has the appearance of attraction, while the strongest shows 

 an abrupt termination of the positive column in the neighbourhood of 

 the point, followed by a negative halo, and then by a recommence- 

 ment of the positive column in the direction of the negative terminal. 

 Each of these sectional discharges is in fact independent and complete 

 in itself, and they are due to impulses of positive electricity thrown 

 into the tube from the air-spark. At the positive terminal these 

 impulses are thrown directly in ; at the points of connexion they are 

 due to induction, ah extra. The negative part of what was originally 

 neutral meets the positive column, and satisfies it as it arrives, while 

 the positive leaps forward to meet the negative due from the negative 

 terminal. 



