The London, Edinburgh and Dublin philosophical magazine and journal of science . variable values, andthat it suddenly changes from one value to another withoutany apparent reason, the working volts of the lamp remainingconstant all the time. If the surface of the collecting-plate is large, say severalsquare centimetres, the potential-difference existing betweenit and the positive electrode is not found to be so muchreduced by attempting to measure it with a galvanometerof about 6000 ohms resistance as it is wdien the collecting-wire presents, as in this lamp No. 1, only a small totalsurface of
The London, Edinburgh and Dublin philosophical magazine and journal of science . variable values, andthat it suddenly changes from one value to another withoutany apparent reason, the working volts of the lamp remainingconstant all the time. If the surface of the collecting-plate is large, say severalsquare centimetres, the potential-difference existing betweenit and the positive electrode is not found to be so muchreduced by attempting to measure it with a galvanometerof about 6000 ohms resistance as it is wdien the collecting-wire presents, as in this lamp No. 1, only a small totalsurface of about one square centimetre. § 12. Experiment 9.—A horse-shoe carbon filament, taking1*3 ampere of current at a wwking-pressure of 42*5 volts,had a middle plate made of a long piece of platinum wirebent up in a zigzag shape so as to form a rectangular-shapedgrating (see fig. 8). The object of this was to ascertain Edison Effect in Glow Lamps. 75 whether a middle plate offering a surface pierced with manyapertures was as effective in producing the current as a solid plate of about the same general outline. Practically it wasfound that this was the case. The magnitude of the currents obtained at various workingvoltages are of the same magnitude approximately as in thecase of a lamp like No. 4, that is to say some 3-4 milliamperesat full incandescence. § 13. A set of experiments was then undertaken with theobject of examining the special effect of varying the positionof the middle plate, and a series of lamps was used in whichplatinum or aluminium plates held on platinum wires wereplaced in the lamp bulb, or in tubes opening into it, in variouspositions. These lamps are generally 50-volt lamps of usualtype, and had single horse-shoe shaped filaments. Experiment 10.—A lamp-bulb had a side tube blown on it(see fig. 9) and a plate about 6 centims. long and 1*5 welded to a platinum wire was sealed into it. Theplatinum plate was placed vertically and edgeways
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