The sun. [volume] (New York [N.Y.]) 1833-1916, 1915-01-24
They Have Most Practical Set Of Sig
nals---What Visitor Saw at Avia-
ton Field at Johannisthal

the gas supply lasts. and it is custom
AIRY to have "a reserve tank connected
up and ready so that 1t can take up
the service when the first one Is eX-
hausted.
This light has visible range of
twenty miles. and 4 candle power of
$500. The pressure of the gas In the
tank is indicated by a gauge and eff
cient means have been provided TO OBJ
viate the chance of an explosion
"One extremely ingenious feature Of
this latter fiashlight is the manner in
which the gas valve is operated auto
matically by the light OF day. When
the sun rises, even though the day he
cloudy. the light is sufficient SO to at
feet the mechanism that the valve
closes and the lamp Is eNtingu.shed.
Again, when the sun sets and dusk
follows, then the same device opens the
valve and supplies the necessary fuel
for the flame.
The sun valve. 30 called. consists Of
a number Of metal strips Of equal pow
ers Of expansion, which are enclosed in
o cylinder Of glass. Half of the slaves
are gilded. while the other half are black
ened so that the light affects them diff
ferently. Therefore when exposed to
the light Of day each set is heated 10 a
different degree and tho measure Of their
expansion varies accordingly. by means
Of lever this expansion Is transmitted
to the valve. which opens or closes the
apparatus.
The waive operates only under the
Influence OF light ray while the heat
rays which do not transmit light. are
absorbed by the glass cylinder. The
sun valve is 80 sensitive chat 10 will
work under the glow OF a very weak
light. But this sensitivencss * not de-
erred ~ the tio shliRht and therefore tho
apparatus Is SO arranged that the gas
Is not shut OF until the fun light Of
day reigns. Consequently the iustalia-
ton is effective when the day j. dark or
, the atmosphere focly. The cost of cur
rent or gas is relatively low. because Of
the very moderate consumption.
an addition to flashlights with sta
tionary girdlc lenses. which permit %.
signalling any designating number, the
German manufacturers also produce re-
volving lights Of many millions Of can
die power. In tine clSe of the latter the
rays OF light are concentrated and pro-
jectcd in a narrow path, reaching from
the horizon to the zenith, Ike "A quarter
Of thin cake stood up on edge. and this
bar OF light. when viewed from aloft.
can be swept around horizontally So as
to cover every point of the compass.
AS the deS isnating number Of a re-
volving light depends On the number of
its revolutions and the Arrangement Of
it's fash openings, and as but few of
the latter can he grouped around one
source OF light, the range of thN signals
is equally limited, being eight al the
most. Therefore lights of this particu-
lar sort are employed only for prime
positions, whore their grea ter brilllancy,
even with fewer flashes, answers their
purpose well.
To-day Germany has these dazzling
beacons at Johannisthal. Bonn. Gotha
konigsberg, Liegnitz, Metz, Posen,
Reinickendurf Schleissheim, near
Munich. and Strassburg. Just as big
lighthouses are generally erected for
mariners nearing a coast, flashlights o.
this sort meet the same general need If
guiding the air pilot and the smaller
lights will serve the more detailed duty
Of marking the way 10 landings, &c,
Just IS the buoys supplement the pur-
pose Of the lighthouse.
While we were still discussing the
merits of these fixed guides for the air
man a youth approached with some
thing Ike a knapsack strapped upon his
back. Our officer guide said:
This young man Is bringing us a
sample searchlight especially designed
for military service and it represents an
effective ana ideal illuminant TIE
whole apparatus. together with fuel FOR
two hours, weighs but twenty pounds
while the officer spoke the young
man quickly took the pack from his
back and set the lamp working, the
light piercing the darkness for dis
lance Of quite 1900 feet. All that was