Iowa County democrat. [volume] (Mineral Point, Wis.) 1877-1938, 1907-06-13
MEASURING LIGHT.
System for Finding Out the Efficien- }
of Gas

System for Finding Out the EftIcIen- J
of Gas.
What does it mean when We say
that gas is required to be a certain
candle pOWer-twenty-two in New
York, sixteen in Boston, fourteen in
London and fourteen and sixteen i'll
other English cities? The ideas of
most peOpIe on the measuring Of light
are extremely vague. says Gas Logic.
Obviously, light cannot be dipped UP
with a quart cup or laid alongside OF
a yard-stick, and rule of thumb would
hardly be a reliable way Of deciding
the amount of light to which a great
city is entitled. Yet until a compara-
lively few years ago it was mole rIle
OF thumb than anything else that cid
decide this important question. + en-
4 casual examination Of the compare
tive size OF the gas pipes in the old
houses and the new of This city will
show that our forbearS we're content
with a less satisfactory Sas service
than We, though, doubtless in con-
DarisOn 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
guesswork about the measuring Of
Eight 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
is a science all by itself. The en-
cyclopedia will tell you that light IS
measured in this way:
If a point source emits in all direc-
tons a quantity Of light NJ, its inten-
sity is said to be MA: that is. the
quantity Of light going out through 81
unit solid angle. This intensity is
written 4. A small surface Of area
A at a distance r from the point
it to the point source SC that the ans;le
between this line and line perpendic-
uIar 10 the surface
And SO on and so on.
But that to the average mind non
scientific, is not Ineligible. II 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
ph0tometric appliances. Ii is dark as
one searches for cOmparisOns-as
TOphet. Everything in the room is
painted dead black and there is not a
bit Of bright metal work anywhere to
catch the light.
Along one side of the room stretches
a high table, with a gas jet at one end,
and at the other end two standard can
dies or standardized lamp runs a hOr-
izontal bar on which is a graduate
scale, and on this bar rests a movable
sighting box.
In this box are two mirrors set at
angles so that a disk placed between
them and whose plane is in the line Of
vision is visible in each mirror thai
is, both sides of it can be seen at once.
L
per forming a star, the differnece in
thickness Of the papers allowing light
to pass through the thin material and
be reflected on the Opaque one so that
some of the light passes through the
disk from the source Of light and is
reflected from the face of the other
disk by the other source OF light.
Thus the intensities of the two sources
of light are in juXtaposition and VIII en-
the sighting box containing the disk
is moved to or from either source OF
light it is found that the figure Of the
star on the disk is invisible when the
two sources of light give equal illuml-
nation on the disk. the light on one
side going through the disk and on
the other being reflected from its sur
face On this sighting box is HAND
or pointer which indicates on the
graduated scale on the horizontal oa-
the ratio Of the gaslight TO the stand
ard
In order to correct any inaccuracy