Edison Effect in Glow Lamp*. 101 



fusion a platinum wire in vacuo exhibits the same effects as a 

 carbon filament, and that it can disturb the electrical condition 

 of an insulated metal plate near it sealed into the same vacuum 

 and tends to bring it down towards the potential of the negative 

 end of that platinum wire. 



On the hypothesis that all these effects are due to a scattering 

 of negatively charged molecules from the incandescent con- 

 ductor, we must affirm that the same process goes on in a 

 platinum wire rendered incandescent in a vacuum, only that 

 the radiation of matter is far greater in the case of the 

 incandescent carbon than it is in the case of the incandescent 

 platinum. 



§ 33. If a lamp is selected having an insulated plate fixed 

 between the legs of the carbon filament, it is found that under 

 certain conditions the electric conductivity of the vacuous space 

 between the plate and the negative leg is much affected by the 

 presence of a magnetic field. If a galvanometer, preferably a 

 movable coil galvanometer, having a resistance of about 500 

 or 600 ohms, is connected between the middle plate and the 

 negative leg it will show but little current passing when the 

 lamp is incandescent at normal temperature. If the volts on 

 the lamp terminal are raised so that the filament is brought 

 into a state of incandescence corresponding to about 2*5 or 

 3 watts per candle, then the galvanometer will show a small 

 current passing through it. If then a horse-shoe magnet is 

 held so as to create a magnetic field the direction of which is 

 across the space between the plate and the negative leg, the 

 current indicated by the galvanometer immediately decreases 

 considerably. This happens irrespective of the direction of 

 the field so long as it is across the direction of the line joining 

 the negative leg and the middle plate. This indicates that 

 the presence of this transverse field increases the resistance of 

 the rarefied gas. The galvanometer current responds to the 

 presence of the magnet in a manner which shows that the 

 resistance to the flow of the current through the gas is 

 increased by creating a magnetic field at right angles to the 

 line of the current. The general fact that gaseous resistance 

 is increased by such a transverse magnetic field has been 

 already noted and described by Professor J. J. Thomson. The 

 behaviour of bismuth as regards electrical resistance in a 

 magnetic field is strikingly similar. 



The "jumping M of the current from one value to a higher, 

 which has been already mentioned, appears to be due to some- 

 thing equivalent to a sudden change in the resistance of the 

 space between the negative leg and the middle plate when the 

 lamp is in action and at high incandescence. The fact of 



