The Saint Paul globe. (St. Paul, Minn.) 1896-1905, 1904-02-28

that distance books could be ready by its
light.
improvements In Lighthouses.
Few persons outside Of those connected
with lighthouse establishments realize the
marked improvements which have been
made in lighthouses, widening their sphere
of usefulness. Prior to the year 1922 the
optical apparatus used In the best equip
ped light houses was a silver plated para
bolic reflector. The power of first order
reflector light of sixteen refiectors ranged
on a frame having four faces, was equal
to SS40 candles. In place of the refiectors
today lenses are used, which multiply the
light of an oil lamp to many times that
or the early refiectOrs, and which con-
verge the rays above and below the CEN
ter of the light until they are parallel to
tnose thrown out from the center, the
whole going forth in one straight shaft
SO difficult is it to make these lenses and
prlsms that there are only four places in
the world where thew are made-one in
England and three in France, the home of
lenses. One of these sets of lenses was
given TO one Of the most prominent Amer
lean optical firms to copy, but after nearly
a year of experiment the attempt was
abandoned. Therefore Uncle Sam Is COM
PEELED to buy most of his equipments in
Europe. The cost of the lenses runs as
high as $50, 600. Even when repairs are to
be made 1t is necessary to return the
lenses to the makers. One would think
that they. being of heavy glass, would
seldom require repairs, but the visitors to
SOAlS VI Tie ldI lighthouses on the Long
island coast have doubtless observed how
badly nicked are the keen edges of the
prlSmS. The keeper of one of these light
houses was asked for the cause Of the
damage.
1.-The birds did it." he replied. when
the geese and ducks are migrating they
Dash themselves against the plate glass
outside, and when the glass breaks the
pieces ny against the lenses and break
Them
This plate glass is of considerable thick
ness, but the birds strike it with a force
that not only breaks the glass panels,
but kills the birds themselves. The keep
er said on these occasions he invariably
had game dinner the following day.
The great difficulty in constructing the
lenses lies in combining the prisms in
such way that every ray shall lie paral-
lei with every other ray from their source
to the pilot-house of a vessel just appear
ing over the horizon from ten to twenty
f1ve miles away. The variation of slight
fraction of an inch at the lens would be
exaggerated many thousandfold at the
horizon
The lens of the Highland light is of
the bivalve type. SO called because it con-
slsts of two convex sets Of lenses and
prlsms, Joined at the edges by heavy brass
bands which concentrate all the light into
TWO beams. BY means of this cOncentra-
ton more intense light is obtained from
a, given size of lamp than is possible from
the older style of lens distributing the
light throughout the entire $50 degrees.
The flash is usually obtained by moving
the entire lens around the light on ball
bearings. The apparatus at the NavesinR
Highlands weighs forty-f five tons, and
could not be moved on ball bearings readi-
ly; therefore 1t Is f1oated on mercury,
and can be moved with a touch Of the
| finger.
Passengers on the Boston boats have
observed on the sandy bluff on the east
side of Cape Cod three stubbed white
| lighthouses with black lanterns. These
are relies of the old method of conveying
information to the mariner regarding the
| particular part of the coast he was APP
| preaching.
The Matlnicus Light.
The seaman knew when he sighted these
three lights that he was abreast the center