The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1855-02-09

LECTURE BY lieut.. BARTLETT, U. 8. y.

LECTURE BY LIEUT.. BARTLETT, U. ST.
The American Geogr aphicals Society gave an exhibition
Of the newly invented Fresnel light, 1t the Hall Of the
University, last evening. The light shown was fine
specimen Of the second class. After II had been OF.
hibited, Lieut.. Bartlett, U. s. N, delivered q lecture
upon the subject in the small chapel He commenced
BY saying that the conditions to be fulalled In SEQ lights
were that they should be placed upon such points that
they may be safe guides for the mariner by which TO
hold his course. These FIRST class lights should have the
highest power Of illumination and the greatest fash, 50
that they may not be mistaken for other lights. The
great light having shown the mariner his course, a
smaller port light shows the pilot his berth. The Fres.
uel system answers all these conditions. Up TO a late
period the lights were made by piles Of wood or coal.
This was replaced BY the Argand lamps with the para.
bolic reflector. These give o strong light at . small
angle, but II there we're thirty lamps the effect would
mot be equal to that OF O third rate flashing Fresnel
light. The French government deserves the credit Of
the new system, which5was the idea Of Fresnel, in making
thus obtained the mode Of multiplying the ipseasis. y
n~h+ II was necessary to increase thu volunS az l,.ht
X, a,,t asbi,,saeut show. me Light visible to the naked
eyeata distance Of ni.,, mufsl Inc volume Of Light was
increased BY placing four wicks WI = current q air y.
tween them. This has since been 30 impro ..ea tRAt tia
Frssnel light ia now equal to 9 5000 Argand OF CsrcelIamps,
Arsgo, before the French Academy, in 1879, gave a des.
Arago had used at sixteen leagues distance was not equal
10 the present Fresnel Light, because the lens In many
pieces or steps was then imperfect in construction. The
lecturer made a diversion to show that thsre was no
truth In the claim Of the Enghsh to the priority Of In
v~ention, Mr.. Stephenson claiming TO have been the arst
to make q lens with concsntric rings. The largest Of
these rings has . diameter Of ten feet, and tho cutting Of
IT b An immensely difficult operation. The cutting and
polishing occupy thres weeks. The rejecting lights In
France were much better than ours, but mot By any
means equal to the catadioptric system. The nrst light
on the fresnel plan was put up at Cerduan, on the coast
Of France; and thus In 1885 was done there what Mr..
Stephenson claims 70 have discovered In 1850. Since the
Cerduan light was set up the improvements In the man.
~ufacture Of the Frcsnel light have been great. A power
has been obtained IN intensity, brlliancy and continuity
Of light which would have surprised fresnel himself.
The msriner now has q dxed and q flashing light At the
same time, for the distance Of fifteen marine leagues,
and the duration Of the nAsh has been increased 10
fourteen seconds. There In no wearing out TO these
lights. The apparatus viii be as good . hun
dred years hence A. 10 IL COW. We have
one Of the best Of these lights (shown at
the Crystal Pslace) and now set mp on Caps Hatteras.
The maker Of this Light carried out the idea Of Fresnei
Of total refrsction. In this Light we have ons ST.
multaneous column Of projected Light, and the design
10 increase and ~lengthsn the flashes was entirely sue
cessfui. The eclipse IL equal 10 the fash, and the light
cannot bs mistaken for any other, which Ia an important
condition. An improvement hes been projected By means
OF cafadioptrc ~renectors, Instead Of plated. The ex-
pepss Ia much greater, however, and the nee re6ectors
have not been used. The rehectors are used on
the land rside, where IL IL not recessary 10 lila.
miuats the whole horizon. With regard 20 the pro.
rress Of the improvement In the Unitsd States the
lecturer sAid that the attention. Of the department had
often been called 10 tae suresisrity Of the corduan lght.