Vacua, and on Coronoidal discharges. 



471 



it was made to swing back and forth as if acted upon by a wind 

 coming from the path of the discharges. This action was 

 hardly perceptible in high vacua but increased quite consider- 

 ably with the increase of the gas pressure. It may, however, 

 be due to a great variety of causes, like peculiar distribution 

 of pressures due to a peculiar distribution temperature ; so- 

 called apparent (in my case continually varying) electrostatic 

 charge over the surface of the mica, etc. 



IV. ON CORONOIDAL DISCHARGES. 



Wishing to perform additional experiments which could 

 throw some more light on this particular feature of the dis- 

 charge, I constructed the apparatus given in fig. 10. A large 



Fly JO 



glass bulb was coated with tin foil along those parts of its ex- 

 ternal surface which would approximately correspond to its 

 temperate zones, its neck being one of the poles. This tinfoil 

 coating had a wire g attached to it by means of which it could 

 be connected to the pole of the induction coil, and serve as an 

 electrode of the bulb. The other electrode was a brass sphere 

 a attached to a brass rod b. This brass rod was surrounded by 

 a glass tube c d and the space between the two was filled with 

 sealing wax. In this arrangement the pressure could be varied 

 between very wide limits (up to about 100 mm ) without running 

 the risk of refusal on the part of the induction coil to force a 



Am. Jour. Sci.— Third Series, Vol. XLIII, No. 258.— June, 1892. 

 31 



