26
THE MASS OF THE ELECTRON
2—4. _ Kirchner’=s Modication of the Wiechert Method.—As
—
shown in gure 2—4, a collimated beam of electrons paSses directly
to the uorescent screen S, unless deected by electric elds at
Cl or Cz.
_
A vacuum tube oscillator O produces alternating
_
potentials of very high frequency (say 107 cycles per second) simultarieously. across the two sets of deecting plates. As the elec.trons pass through C1 they are deected back and forth rapidly
in the plane of the paper so that only those
which had passed
thr0ugh,C1 at the instant when its potential was zero Will be able
‘togo through the central hole in the diaphragm D and enter the
secondcondenser Cz.
Thus, spurts of electrons will enter C2, one
each half cycle of the oscillator. If, now, during the time !
fe o
…
'
_l‘lllu
_
v
_
FIG. 2—4.
method.
_
;
required for.the electrons to travel from Cl to Cg, a distance L,
,
on the second Condenser has again returned to zero,
the ele‘çtr0ns
continue to travel
to prOduce a
fsingle spot
light at the center of the screen,
_
If ,theftinae £or the
electrons to travel this diStan-ce isless than" one… half cycle(orany
>
mult1pletheϨf),a pOte'ntizil difference W1113X1Stacr088thesecQnd
latesanthe;rdèmns
f0rmtWOdlstmctspots
°thescreenThlsmaybeseenfromgureZ—SThuselectrons
WhichPassthr®ughüatlaredeectedbrapotentlaïacresscz
lszemlust“themstanteachhalf°Ycïegrüup0felectmnsarrwes