The Ketchum keystone. [volume] (Ketchum, Idaho) 1885-1899, 1895-08-03
LIGHTS ON THE OCEAN.


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The Governments - eevseal Na&a1n1
/ Deeply Inesssstea n Asssetafnlhg
which Ars &hs b. LAgAHs
for eae1als.
Some intekeotink and valuehie In
formation regarding the color ard vist
bflity q the iiahtsss sst ses has beenpab-
lished by the naval photographic Office
as result Of special Investigations
undertaken by officers Of this goyernr
ment, Germany and the Nethetlan1B.
A marine observatory in Germany in
this connection tested some three thou
sand running lights actually in use on
board ships and found that two-thirds
of them failed to meet cqndf idns pre-
scribed by the international maritime
conference held in Washington in 1889.
It was then stipulated, says Wash
ington letter to the Baltimore Sun, that
the word visible" should mean visible
on dark night with Z clear atmos-
phere. The Germans have further
pursued the inquiry by a systematic
series of experiments. A light was set
up on shore and observers embarked
on board steamer which ran over q
well-buoyed course. The point at
which the light ceased to be visible
was noted by each observer independ-
emily, as well as the point at which it
first appeared on the return trip. The
mean of the several observations was
taken as the limit of visibility of the
light under observation. The naval
photographic office sends out the fol-
lowing:
The American experiments under
taken at Long Beach light station gave
the following results in. very clear
weather. A light Of 1-candle power
was plainly visible at / nautical mile,
and one of 3-candle power at . miles. A
10-candle power light was visible with
q binocular ut miles, one of 90 cam
dies family at 5 and one of SS candles
without difficulty at the same distance.
On second evening, exceptionally
clear, white light of 3.2-candle power
could readily be distinguished at 8.
one of SO at and one of 17.2 at miles.
The governmental experiment con-
Quoted at Amsterdam gave the follow
ing results: A light of 1-candle power
was visible at nautical mile, S.5 at 2
and 16 at miles.
The German observations represent
more varied conditions and a large
number of experiments with lights Of
widely-different character and inten-
sity.
In experiments with colored lights it
is only necessary to use the green, as
it has been conclusively proved that if
light of that color fulflls the required
tests, red one OF the same intensity
will more than do SO. Comparisons of
the observed and computed values of
the visibilities of green lights disclose
the fact that the calculated are smaller
than the observed for short distances
and greater for long ones; in other
words, the green rays are subject to
greater absorption by the atmosphere,
even when perfectly clear, than rays of |;
white light. Hence it is that instead Of !
being proportional to the square of root
candle power, rs in the case.pf whita
lights, the intensity Of green lights is
to the cube root of the
same, and the factor for multiplying
this quantity is, as-determined by Ger
man experiments, 0.8O, the distance IN
miles at which green hight or single
candle power is just visible.
From this r6le the candle power re-
quired for green light to be visible at !,
one, two, three and four nantical miles
is two, fifteen, dfty-one and one hpn-
dred and SIX respectively. The expert
ments at Long Beach cited ADORE gave
for green light 80 candle power A64y
visible at one mile, and 23.5 clearly 81 |
two miles, these results, however, be-
ing from limited number of. expert !
ments The German trials were much
more numerous.
The extraordinary rapid diminution
Of the visibility Of the green light with /
the distance, even in good observing
weather, and the still more rapid de-
crease in rainy weather of 3 character
which will butslightly diminish the In
bensity of white light, show that i fs
81 the utmost Importance 10 seleck fer
she glass q shade of color which will
with the intensity Of the light
IS little as possible. The shade recon-
nended is pale blue-green. Yellow
yreen and grass-green should not be
employed, as they become indistin-
yuishable from white at very short /
distance. For the red considerably
wider range Is allowable, but a-cop-
,ery red is probably the best.
With regard to the loss which the
light suffers in being transmitted by |
he glass, testamede nhoev that this yAsf
les from hcurteen per cent. ID the c&se
# perfectly clean glass to fifty-one
YER cent. in the case Of one IN the
moky condition due to nights burn
no.