18—15.
PRINCIPLE OF EXPANSION'CHAMBERS
433
dry gas has
a wider plateau than one containing a trace.of water
vapor; Wlth hel1um,
the plateau is absent or negligible unless a
trace of oxygen 13 present; the at—
mess of the plateau depends Upon
1500
.
-
.
…
the pressure of the gas in the tube.
.
,a
EXPANSION CHAMBERS
:*
M/
18—15.
The Principle of Ex%
'
=
f
pansion Chambers.——A simplied
Ë
'
'
diagram of an ' expansion chamQ
/
_
ber
(that of C. T. R. Wilson,
%
Mao”
.
used in 1911) is shown in gure
Ë
18—13.
A large cylinder of glass
:
.
.
oo
_
G (10—20 cent1meters d1arneter)
0'
PRESSUR£, CM« OF M53çygy'
I0
.
is Closed at one end by â glass FIG. 18—12.
ThreSholdwoltage
'
_
WÏHdOW
(W) and at the other pressure curves of a counter tube.
'
end by a piston (P) to form the
‘
'
chamber.
A trace of water in the chamber keeps theair
When the piston is suddenly pulled down, the temperature in the
_
chamber drops below the
Then, small drops of water
form on condensation centers such asdust particles
The ' ‘
-
cloud of water dr0plets -«is illum‘i—_
'
_
/
W
'
n‘ated by light (L) from the Ïsi_deä
through… the
.
P
‘
‘
! The ‘drbpl_ét}sÏimayfbe allQWed-to
_
… È settleslowlytothebottomofthe -
‘”
-
-
?
“
%
formedonchafgedPamdesbe
“
;
’
-
“
eleCtceldbetweenthemetal
'
-
Fm. “18—13;
A simple expansmnPlStonandthemetalrlng®
‘
chamber; … Whenfatllcomîensatl®nœnœrs
;
“
Α3XPaînsîb
‘