The Cambria freeman. [volume] (Ebensburg, Pa.) 1867-1938, 1895-08-09
LIGHTS ON THE OCEAN.
Interesting Experiments with the
Visibility of Different Colors.
The Governments of Several Nations
Deeply Interested In Ascertaining
Which Are the Best Lights
for Signals

Some interesting and valuable in
formation regarding the color ard VI>l-
bilitv of the lights at sea has been pub
lished by the naval photographic office
a. a result of special Investigations
undertaken by officers of this govern
ment, Germany and the Netherlands
marine observatory in Germany IN
this connection tested some three thou
sand running lights actually in u.s. on
board ships and found that tw"-thlrdS
of them failed To meet conditions pre-
scribed by the international maritime
conference held in Washington ia l>e"
1t was then stipulated, says a Wash
ington letter to the Baltimore sun. that
the word visible" should mean visible
on dark night with a clear atmos-
phere The Germans have further
pursued the inquiry by a systematic
series of experiments \ light was set
up ON shore and observers embarked
on board a steamer which ran over
well-buoyed course The point At
which the light ceased To Ice visible
was noted by each observer lndepend-
emily, as well as the point at which II
first appeared on the return trip The
mean of the several observations MAS
taken as the limit of visibility of the
| light under observation The naval
| hydrographic 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 l-candle power
was plainly visible at l nautical mile,
and one of 3-candle power at : miles y
lO-candle power light was visible with
1t one. of can
dies family at 4 and one OF 5$ candles
without difficulty at the same distance
On a second evening. exceptionally
clear a white light of 3.2-candle power
could readily be distinguished at 3.
one of SO at and one OF l1-2 at > miles
The governmental experiment con
Quoted at Amsterdam gave the follow
ing results: A light of l-candle power
| was visible at ! nautical mile, 3-5 at =
and 10 at miles,
The German observations represent
more varied conditions and Il large
number of experiments with lights OF
widely-different character and inten-
sity.
In experiments with colored lights IL
Is only necessary to use the green a.
it has been conclusively proved that II
a light of hat color fulfillS the required
tests a red one of the same intensity
will more than do 50. Comparisons ot
the observed and computed values o
the visibilities of green lights disclos,
the fact that the calculated are smaller
than the observed for short distance:
and greater for long ones; in othel
words, the green rays are subject &
greater absorption by the atmosphere
even when perfectly clear, than rays q
white light Hence IL Is that instead -
being proportional To the square OF r""
candle power, as in the cas- of whit
lights. the intensity of green lights I
proportional To the cube root OF tn
same and the factor for multiplying
this quantity is, as determined 10y GvI
man experiments, go, the distance d
miles at which a green light or a singl
candle power is just visible.
From this rule the candle power r.
quired for d green light t. be visible q
IS one two. three and four nautical mile
+ is two. fifteen, tifty-one and one hun
dred and six respectively The eNp"r
g ments at Long Beach cited ah""e gaN
for green light 81 candle power falrl
|, visible at one mile, and 2s.5 clearly Z
= two miles. these results, however. h
ing from a limited number of eNper
= ments. The German trials were niue
The extraordinary rapid diminutio
! of the visibility Of the green light wl'
- the distance, even in good "bservlT
weather. and the still more rapid q
=, crease in rainy weather of a eharaet
a which will but slightly diminish the 4
- tensity of a white light, show that II
~ of the utmost Importance to select I
the glass a shade of color which "
: interfere with the intensity of the liz
as little as possible. The shade reco
mended is pale blue-green- 1eilo
green and grass-green should not
,r- employed as they become indist
nj guishable from white at a very sh,
A.. distance For the red a considerat
Si- wider range is allowable. but e'
nd perry red is probably the best.
TX With regard to the loss which I
he light suffers in being transmitted
rat the glass tests made show that this
ily ries from fourteen per cent. IN the e;
,g- of perfectly clean glass to fifty,
nd per cent in the case of one IN
tly smoky condition due To a nights Gu
for ing.