Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1896-08-13
FRENCH LIGHT-HoUsE SYSTEM.
Number, situation, Range, and
Power of Lights.

publishing I'm Engineering an elaborate
and valuable series of papers upon coast
and lighthouse illumination in France.
with comparisons between the lights OF
France and England.
Luminous power and range are. as Is
well known, greatly affected by the vary
ing density or degree OF transparency OF
the atmosphere. The French Lighthouse
Department has accordingly calculated
and laid down in an official list the Ium-
nous ranges of all the coast and harbor
lights on the shores of France. under
average and hazy conditions of the at
mosphere. Mr.. Du Richie Preller con-
structs a diagram of these ranges "nd
then deduces from 1t some interesting
general points
The first is that the luminous range OF
powerful lights rapidly loses I'm ratio as
their luminous power increases. For
example, light of 100000 candle power
i'm the British Channel has, I'm average
weather. a luminous range of about "A
nautical miles. while If the light is in
creased to a power OF 100000 candles
the luminous range is only miles more,
OF 10 miles.
A second conclusion is that. in lights
up to 1000 candle power. the luminous
range in average weather is. broadly
Speaking. about double that I'm hay
weather while i'm lights above 1000 can
die power 1t is approximately as to l.
A third and striking conclusion IS
that the luminous range OF light OF
500 600 candle power in the Mediterranean,
forty-fOur miles, is equal TO that or
). 100000 candles in the Channel, equal to
a ratio of one to ten" Hence 1T is added,
with the exception of the electric flash
ing light OF Planter, near Marseilles, OF
10000 candle power. the most powerful
mineral oil lights recently installed on
the French, Corsican, Algerian ana
Tunisian coasts Of the Mediterranean do
not exceed IS 900 candle power, having a
luminous range of about thirty miles IN
average weather On the other hand, In
the Channel, and in the Bay OF I;scay'
the largest mineral oil-lights have lumi-
nous powers up TO about 10000, and the
electric Qightning-hash). lights up to
y. 10000 and 100000 candles.
The maximum height Of French light
house towers-that il. the height OF the
focus above ground-varies from about
fifty to seventy metres, the highest be
ing the Barheur electric tower on the
Channel. 233 feet; the Penmarch and the
Codouan. on the Bay OF Biscay. 207 feet,
and the Planter, on the Mediterranean,
1873 feet But some towers are of course
on very elevated ground, so that taking
the height OF the focus above the sea
level. the highest light, that OF Cape
Brearn. Is 75l feet above the high water
sea level. while its luminous power Is
5000 candles, and its luminous range
twenty-five miles. The height Of the Cape
Camarat light Is 426 feet, that or Fatou-
Vile is 40 feet. and so the list goes down.
The Cape Brearn is an oil light, and The
geographical range or direct Visibility OF
such lights on high elevations Usually eN-
coed their luminous range. But the re-
verse Is usually true OF electric coast
lights. For example, the Selikncwa group
flashing light OF Ushant. Z5 feet above
the sea. with a luminous power or
6.5OO.O 600 candles, has an ordinary luminous
range of fifty nautical miles, while its
geographical range varies from twenty
one TO twenty-seven only. according TO
the elevation Of the observer. In such
cases therefore. the effective range or
direct visibility Of a light is its geographi-
cal range. or horizon distance, beyond
which the observer sees not the light
itself. but only the glare OF the hashes
as they ilumine the sky.
The French electric lights now number
only thirteen. or very few compared with
the mineral oil, or even with the gas
lights. The flashing lights number but
occulting. and alternating lights, the
whole making a total for the French, In
GLIDING Corsica, Algiers. and Tunis, or
600 lights But the flashing lights have
a total luminous power Of 7O,S36,SiO can
dies. against go. $50 candles for the other
lights which are about six times as nu-
merous. II the three electric lighting
flashlights now in course Of construction
10 replace the same number OF electric
fixed lights and aggregating HoOO,V0
candle power, are added, the total Tor the
$50 French lights will be in round hgures'
l49. 900 900 candle power. There are also In
course of installation six mineral oil
lighting flashlights.
Comparing British and French lights, 1t
appears that the former, as 10 the maxi
mum heights, both Of towers, and OF the
focus above the sea level, are below
those on the French coasts. None OF
the British towers reach 200 feet,
though Bishop Rock is 49, Eddystone l6S,
Sker~yyore 1853. and Chicken Rock 1b. The
highest light above the sea level is that
of Barra Head, Csc feet. followed by
Lundy. 54O Cape Wrath, 400; South Fore
land. ga: Dunnet Head. 5i6; ST. Bees, 1876;
and Null OF Galloway and Great Orme's
Head, each 325 feet.
The number of lights on the British
and Corsica. But while the luminous
mower Of the former is 1S.7O6.55O candies
that OF the latter is 7l,l45,l 100. In oil and
gas lights the British Isles have about
one third more mean power per light,
but in electric lights, France and Corsica
have 26 as much mean power as Great
britain. Moreover, the total British sea-
board is $500 nautical miles, while that
OF France and Corsica Is only l,6s2, so
that the former averages light Tor each
five miles. and the latter one for a niue
over three miles. There are some small
local lights. both in England and France,
which are not under the jurisdiction OF
the lighthouse departments, and hence,
are not reckoned in these comparisons
Light vessels are included, but luminous
buoys excluded in them.
The tables Of the seventy-fve cher
French lighthouses show that the max
imum duration Of flash is seventeen
seconds. that Of the single flash light. at
Cape Bona, and that the minimizing Is
the uniform one-tenth OF a second, known
as the lightning fash. There are the red
the red and white. the group fash, and
single flash. the fixed, and the fixed and
eclipse. The average distance between
these lighthouses is about 30 nautical
miles in the Channel, IS in the Bay OF
Biscay. 10 on the Riviera, and I'm Corsica,
and about so nautical miles on the Afri-
can coast. In other terms the luminous
ranges, or, as the case may be, the geo
graphical ranges of the principal lights
intersect each other.
Mr.. Du Richie Preller gives some account
also. OF some OF the latest Improvements,
I'm lighthouse apparatus. Cape dAntifer
is a conspicuous headland near Etretat,
between Fecamp and Havre. The light
house on II is 300 feet above the sea
level, and has a siren worked by com
pressed air in the upper part OF the