Vernon County censor. [volume] (Viroqua, Wis.) 1865-1955, 1907-06-19
MEASURING LIGHT.
System for Finding Out the Efficien y
of Gas

y
of Gas.
What does it mean when We say
that gas is required to be certain
candle twenty-five in New
York, sixteen in Boston, fourteen in
London and fourteen and sixteen il
other English cites: The ideas of
most people OH the measuring of light
are extremely vague. says Gas Logic.
Obviously, light cannot be dipped NJ
with quart cup or laid alongside of
yard-stick, and rule of thumb would
hardly be 4 reliable way OF deciding
the amount of light to which a great
city is entitled. Yet until a compare
lively few years ago it was moIe rile
of thumb than anything else that Gld
decide this important question. r IN
casual examination of the compare
tive size OF the gas pipes in the old
houses and the new of this city viii
show that our forbears we're content
with a less satisfactory gas service
than We though, doubtless in con-
paFison with the old-fashioned lamps
and candles. the modest gas JET Of
the SOS seemed brilliant beyond
words
In these days, however. there is no
guessworlx abcut the measuring OF
light. 1t is gagged as carefully and
accurately as a dainty lady's ribbons
or a physicians prescription. The
systems by which gas is measured
have all grown up within two genera
tons
Photometry-the measuring OF light
lis a science all by Itself. The en-
cyclopedia win tell you that light IS
measured in this way:
IF point source euaits in all direc-
tons quantity n light M. its inten-
sity is said to te Ma: that is, the
quantity of light gong out through a
unit solid angle. This intensity s
written r.. A small surface of area
A. at a distance r from the poin.
source and inclined to the line joining
it TO the point source Sc that the ans ie
between this line and line perpenSic-
ular 10 the surface
And SO on and so on.
But that to the average mind non
scientific, is not inteiligible. IL IS
much more interesting TO see how The
thing is actually done
in laboratories of the gas company
there is one room set apart for the
pl.otometric appl.an Ii is dark a.
one searches for comparisons--as
Tophet. Everything in the room Is
tainted dead black and there is not a
bit Of bright metal work anywhere to
catch the light.
Along one side of the room stretches
high table, with a gas jetat one end,
and at the other end two standard can
dies or standardized lamp runs hor-
izontal bar on which is a graduate j
scale. and on this bar rests movable
sighting box.
In this boy are two mirrors set at
angles SO that disk placed between
them and whose plane is in the line of
vision is visible - each mirror hal
is. both sides of it can be seen at once,
The disk consists Of TWO kinds Of pa
per forming star. the differnece in
thickness Of the papers allowing light
to pass through the thin material and
he reflected on the Opaque one 50 that
some OF re light passes through the
d SIX frola The source Of light and is
reflected om the face Of the other
disk By the otlcr source Of li2ht
Thus the intepsities Of the t~'2 sources
.of light are in iuxtaposition and VIII IN
the sighting box containing the dist;
is moved TO or from either source oi
light II Is found that the figure Of tie
star on the disk is inyis bic when the
two sources Of light give equal ilIumi
nation on the disk. the light on one
side going through the disk and on
the other being reflected from It's s1i.
face. On this sighting box Is hand
or pointer which indicates on she
GRADUATED scale or the horizontal ba-
the ratio Of the gaslight to the stand
ard
In ORDER to correct any inaccrracy