The Republican journal., 1892-12-01
Avoid Collisions at Sea.

INVESTIGATION OF THE VISIBILITY OF
WHITE, RED AND GREEN LIGHTS.
When the International Marine Confer
ence recommended system of lights on
vessels as preventive of collisions at sea
there became necessary the examination
of the power and intensity of lights and
the solution of the problem what was the
least candle power at which lights of va
rious colors could be clearly seen at def
mite distances Certain rules were laid
down by which vessels under way and at
anchor would display certain prearranged
''visible'' lights. The matter of deciding
just what visibility meant was left to the
lighthouse board of the treasury depart
ment, and a committee of experts We're
selected to conduct experiments.
A uniform method of signaling on ships
is quite important. 1t is found that there
should be one standard by which the light
issuing from a lantern should be measur-
ed, the colors being distinct. Up to the
time the international Maine Conference
settled in its mind the value of a system Of
signaling there has been no official deter
mination of the power and intensity of
lights SO that the experts had an untrav-
ersed field before them.
The experiments which We're to deter
mine what was best for use by the mer-
chant marine as anchor and running lights
We're conducted at the Long Beach Bar
Light Station, New York Three lanterns,
fitted with red, white and green lights re-
spectively, were placed on shore, and OBJ
servatons We're made of them from dis
tances of one, two, three, four and five
miles from the land. Each lantern was
Jo1 Al +,l
the variation OF candle power from one to
4:. The experiments We're considered
satisfactory except that the light from the
lighthouse interfered somewhat with the
result. In these experiments the white
light was most satisfactory
On the first nights observation the
weather was clear and very favorable for
seeing lights. AT one mile the red light
at l. - candle was not visible, while the
white light at l candle power was clearly
visible. At the same distance the red
light at l. IS candle power and the green
light at SO candle power We're still vsi-
BILE; the red light at 2.2O was barely visi
bic; the green light at ?. 10 was very faint;
the red light at 800 was fairly visible
the green light at 800 was brighter,
but not sufficiently distinct
At two miles the red light al $50 can
die power could not be seen, and was
barely visible when the candle power was
increased at that distance to 5. 70. At two
miles the green light, at candle power,
was invisible, and could be indistinctly
seen when the candle power was increased
to 1850. The red and green lights, at
II. 10, at two miles distance, We're visible,
but not distinct in color, and when the
candle power was increased to IS. 20 the
lights were not fully distinct At two
miles, with a candle power of 20, the red
and green lights were distinct, white light
at 3 candle power, from the same point of
observation, was clearly distinct
At four miles the red light at - candle
power, the green light at II, and the white
light at 10 We're easily distinguishable
through glasses, but invisible to the naked
eye.
At five miles the white light at % can
die power was family visible, at 33 clear
ly visible, and at 43 distinct.
On the second night observation the
weather was cloudy, with a few patches
only of clear sky, and no moonlight. At
one mile the red light, at l. 10 candle
power, was indistinctly visible, while the
green light required =. 10 candle power to
become family visible, and the white light
required only 1.04 candle power to he seen
satisfactorily. At two miles the red light
was barely observable at ). - candle pow
er, ard the green light indistinctly visible
at 10. 80. and ~. 40 was the least power for
a clear color The red light was distinct
enough at two miles at d candle power of
$3.50 the white light at three miles was
distinct at so, at miles at $50 candle
power, at five miles at II. 80 candle power
= IL Il .
determining the least candle power at
which colored lights could be seen at def
mite distances is not capable of Il rigorous
solution. In the first place, the eyesight
of different observers varies, and the light
ly visible to one, while it would be indis-
tinct to another, and might be i'll
visible to third. Then. too the nature
or clear, would have a considerable int1u-
ence on the range of visibility of the lights,
although the night of observation was APP
parently clear. In the case OF colored
lights, red OF green. the amount of alb
sorption would increase with the density
of the color of the glass, and this would
also cause much variation in the range of
visibility with lights of the same candle
power behind it.
These conditions had to be taken into
consideration in determining minimum
candle power, and care had to be taken in
the decision that Il proper margin of safety
was allowed. The results Justify the re-
commentator that a white light of one
candle power could be used for one mile
distances. of two candle power for two
mile distances and 30 candle power for five
mile distances. 1T was evident that less
than one power Of candle could be seen
one mile; still it was thought hardly worth
while to use a power less than one candle.
The red light ut one mile should have four
candle power and at two miles 40 candle
power and the same candle power was
recommended for the green light.
Colored glass absorbs - per cent. of the
light. This makes it difficult to compare
white with colored lights and there would
probably be different results in the obser-
vations by different men. There is a de-
crease of the percentage OF loss as the in
tensity of the light increases and this cir
cumstance is probably due to the fact that
with the lower candle power the brightest
part of the flame is used. while with the
higher power the upper and lower parts
OF the flame come into view and those
parts contain more red and green rays.
Whitter's old homestead, ut Haverhill,
Mass. has been purchased by James II.
Carleton, OF Haverhill, and will be pre-