_
arrangement shown reduces scattered light from the edges of the
lenses, particularly those near the source. The apparatus is used
in a darkened room.
Use a lantern slide projector with a 400 to
500 watt lamp, With the projection lenses removed. The lenses
Of gure 4—15 may be very crude, such as from the ve and ten
cent stores._ The prism P is a large, glass or carbon disulphide
(CS2) type With faces four centimeters or more on the side,‘ the
larger the better. Liquid solder has been found satisfactory in
‘
sealing the glass sides to the framework of a C82 prism. The
slits should be about as long as the side of the prism. 81 may have
a Width of ().7 centimeters.
Slits 82 and 83, in cardboard screens,
are used to select portions of the spectrum and are curved to t
IË"
"'A\/ ll
€
L2
/
‘
'
RED
'
// // 3
°°°”
°°°/ ‘ë
w
FIG. 4—15:
Top view of an arrangement for plotting spectral distribution curves
'
'
_
'
of photoelectric cells.
.
.
the curvature of the colored light. 83 is used to reduce the amount
of stray light which reaches the cells; it may be 2 cent1meters
Wide.
The slits are of such Width as to select a spectrumband
,
{about one hundred
Wide, except for the blue region,
'
?
.
necessary due to the low sensitivity of
'
for these wave—lengths. One may use variable
,
.
for 821 of say one millimeter in the red, seven m1111metersl
-
int—he blue.
The average wave—
-
‘
lengthof each
by“ÿmeans of the
spectro—
”l‘“
_
($Foraccuratewœk, One may use the more
com—
in order to
a
_
very
band