Northern Wisconsin advertiser. [volume] (Wabeno, Wis.) 1898-1925, 1907-06-13
MEASURING LIGHT.
System for Finding Out the Efficien: y
of Gas

System for Finding Out the Efficien, y
(, of Gas.
| What does it mean when We say
that gas is required to be certain
Icandle power-twenty-two in New
York, sixteen in Boston, fourteen in
London and fourteen and sixteen in
lother English cities? The IDEAS of
most people on the measuring of light
are extremely vague says Gas Logic.
OBVIOUSLY, light cannot be dipped up
with quart cup or laid alongside of
a yard-stick. and rule of thumb would
! hardly be a reliable way of deciding
1.-THE amount of light to which a great
city is entitled Yet until compare
lively few years ago it was more rlle
OF thumb than anything else that did
ldecide this important question. e en-
IA 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 were content
/ with less satisfactory gas service
than we, though, doubtless in con-
| parison with the old-fashioned lamps
and candles, the modest gas Jet of
1 the SOS seemed brilliant beyond
/ words
! In these days, however, there is no
| guesswork about 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 will tell you that light is
measured in this way: fils
If a point source emits III all direc-
ltions quantity of light Nj, its inten-
sity is said to be Nh: that is, the
quantity of light going out through
unit solid angle. This intensity is
written Il. A small surface of area
/ "A, at distance r. from the point
source and inclined to the line joining
1t to the point source SO that the angle
between this-line and line perpendic-
uiar TO the surface
And SO on and so on.
Bat that to the average mind non
scientific. is not Ineligible 1t 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
photometric appliances IL is dark as
One searches for comparisons
Tophet. Everything in the room is
painted dead black and there is not
bit of bright metal work anywhere to
catch the light.
Along one side of the room stretches
high table, with 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 disk placed between
them and whose plane is in the line OF
vision is visible in each mirror that
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
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 intensties of the two sources
of light are in juxtagositioH and wh 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 illumi-
nation on the disk. the light on one
side going through the disk and or
the other being reflected from its SIN
face. On this sighting box is hand
or pointer which indicates on the
graduated scale on the horizontal bas
the ratio Of the gaslight to the stand
ard
In order to correct any inaccuracy
of the readings ten are taken Of bota
indicated candle power and the gas
consumption in consecutive minutes
and the average of these ten one.
minute readings is used In making tire
final computations Where candles are
used they are carefully weighed be-
fore and after the test to insure the ac-
curacy of their standard Each can
die must consume at the rate OF i20
grains Of spermaceti per hour