The Union and journal., 1861-11-29
Magic Mirrors and Burning Lenses,

magic mlrrorS ana Burning LonSoS.
The famous mirror which Ptolemy Ever
getcs caused to be placed in the Pharos at
Alexandria, is Of the first clsss. The mirror
is stated by ancient authors to have repre-.
scnted accurately every thing that was trans
acted throughout all Egypt, both on water
and on land. Some writers affirm that upon
its surface an enemy's fleet could be seen at
the distance of 100000 PAGES; others say
more than 100 leagues! Albulfeda, in his
description Of Egypt, states this mirror to
have been Of "Chinese iron," which Button
considers to mean polished steel; but wri-
ter in the Philosophical Magazine, 1905 sup
poses the metal to have been iutenog, Chi.
nese metallic compound, capable of receiving
the highest polish. The existence of Ptolc-
my's mirror has, however, been generally rc-
gardcd us a fiction but Father Abbot, In
his Amusemens Phiiosophiques, first published
at Marseilles in 1868. considers that It may
have been at the time the only mirror Of its
kind, and being great wonder, its effects
may have been greatly exaggerated, making
allowance for which, nothing remains "but
that at some distance, provided that nothing
was interposed between tho objects and the
mirror, those objects werc seen more distinct
ly than with the naked eye, and that In the
mirror many articles were seen which, be-
cause Of their distance, were impcrceptible
without It,"
1t is certain that, under such circumstan.
ccs, objects may DO seen ut much greater
distance thaa is generally supposed. Thus,
1t Is stated that tho Isle Of Man is clearly
visible from the summit OF Ben Lomond, in
Scotland, 100 miles distant. Brydone states
that from the top Of Etna mountains, OBJ
jects two hundred miles or may be distin-
guished; and during his visit to TcncriIs,
in 1856, Mr.. piazzi Smyth saw objects at u
much greater distance.
Burning mirrors have been celebrated on
account Of their sizc and extraordinary Of.
feet. One Of these optical machines was the
work Of Stettala, canon OF Milan; 1t was
parabolix, and, acting as burning glass.
inaamed wool at a distance Of Is or IL pa.
ces. Leonard Digges, in his Pdniromeiria.
1871. states that "with glass framed by q
revolution Of section parabolical, have
set tirc to powder half milo or moro dis
tant." In the prosecution of this subject.
the celebrated Napier and Sir Isaac Newton
experinented with parabolical reacctors be-
fore 1913. Vilctte, an artist and optician Of
Lyons, constructed three mirrors about the
year 1870; one of these, which was pur.
chased by the king Of France, was 30 inches
in diameter and Of about feet focus. The
rays of the sun were collected by it into the
space of about one inch. II Immediately set
fire to the grcenest wood, fused silver and
copper in few seconds, aud IN ono moment
ytriGed brick and flint earth. A mirror
even superior to these was constructed by
Baron Won Tehivnhauscd, about 1857; 1t
consisted Of metal plate, twice thick US
the blade Of common knife it was 5 feet
inches in breadth, and its local distance
was 3 feet 6 inches. II produced the follow.
ing effects: Wood exposed to its focus imme-
diately took fire; copper and silver passed
into fusion, and slate was transferred into
kind Of black glass, which, when laid hold
OF with pair Of pnccr. could be drawn
into iilalncnts. Pumace stones and pieces Of
crucibles which had withstood the most yio-
lent cruciblcs. were also yitrifed.
The burning lens constructed by Mr. Par.
ker, many years ago. ut the expense Of 81,
600. was Of flint glass, 3 feet in diameter.
and weighed 2l2 pounds the focal length
being @ feet 8 inches. and the diameter Of
the focus inch. To concentrate the rays
still further. second lens was used, and
reduced the diameter Of the locus to halt an
inch. Under this lens, ever kind Of wood
took FIRE in an instant, whether dry or grcen,
or even soaked in water. The iron plates
grew hot in an instant, and then melted
Tiles, plates, and oil kinds Of Garth were
quickly vitrihed. Sulphur. pitch. and r,si-
nous bodies melted under water. Fir wood e1-
posed to tho focus under water. did not seem
changed, but when broken, the inside was
burned to coal. Any metal Whatever, en-
closed In charcoal, melted in moment the
Ere sparkling like that Of forge. When
copper was melted and thrown down quickly
in cold water. Il produced 20 violent shock
as to break the strongest earthen vessels and
the copper was entirely disipated. Though
the hea, OF the focus was 80 intense a' 70
melt cold In few seconds, yet there was 20
li,,Ic hea. short distance from the focus
,ba, the finger might be placed an inch from
|, withou. ipjary. Mr.. Parker having put
NJ. finger to tho focus to try the sensation,
found !, did not resemble that produced by
Gre or lighted candle. but like that Of a
sharp cut with lsncet.-Seimii6e Amer.
can.