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CHAPTER 4
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—
PHOTOELECTRÏC EMISSION_,
_
4—1.
Introduction.—Electricity is emitted by certain metals
when ultra—violet light falls on theirsurfaces. This is ‘one form
of the photoelectric elÏect.
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The existence of radio waves was predieted in 1864 by_ the
brilliant theoretical work of Clerk Maxwell and was established,
directly and for the rst time—,
Hertz in 1887.
During
the course of his famous experiments,
though he
did not understand, the _photoelectric effect. In his transmitter, a
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spark was producedh‘etween two
_
‘
_
byan induction coil.
of
light
_
a_loop o°f wire whose endSwere;cappedwith
-
,
‘
t
small halls-and placed closéïtoeaCh other to
l. 1,
\
form—asPark gap. When the inductioncoil
—=
«
was turned
and
adjustrents made, ;
-
…
,
.
‘
apPear‘ëd
of? the
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.
…
.
noæd
D
rece1vereventhough1tsgapwasœmparatwelÿ ,, '
-
'
.
Wideprowded theultrawolethghtfr@mthe
À
—' 5 !, spark: of thetransm1tterwasallowedt0fall.aiè
a
7 ”f
*
many0thermetals)connectedmanelectmsœpeasmgure4“1
wasnelassofelectrlütybutWhennegatlvelychafgedthe : 2