Washington standard. [volume] (Olympia, Wash. Territory) 1860-1921, 1872-04-06
A STORY OF SCIENCE.
BURNING MIRRORS AND SUN MAcHlNl

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ror in order to steal by it the fire from the
sun. is only mythical conception, it is
certain that the ancients emplayed at an
early date concave mirrors capable Of ig.
hitting objects at a distance. Euclid men,
tions such mirror in his Catyoptrics, the
science of the reflection of light yet he
erroneou>ly places the focus in the center
of the sphere formed by the mirror. instead
of at the distance ofhalf radius. Plutarch
states in his life Of Numa that the vestal
virgins employed burning pirror iu order
to produce the sacred fire; aud the Ro.
man author, Pliny, appears to have been
we'll acquainted with the fact that mirrors
are capable Of igniting iufammable sub.
stances. But the most remarkable story
in regard to this subject is the assertion
that Archimedes, the most celebrated
mathematician of antiquity, burned up the
feet of Marcellus by means of burning
glasses from the f"rtifications of the city
of Syracuse. Yet many doubts have been
expressed as to tho truth of the story. 1t
has been said, for instance, that Poybius
and Putarch, historians cotcmporary with
Archimedes, fail to say a word about it,
although both speak Of machines invented
by him for the defense of Syracuse.
Later writer's relate that the feet was
destroyed by artificial fire." without,
however, describing how this was done
The first mention that the destruction was
accomplished by means of burning mirrors
dates from the sixth century after Christ,
and was by Trallianus, the architect of the
Emperor JuStinian. 1p the same century
Dion stated that, at the siege of Constan-
lnope, the mathematician Proclus burnt
the feet of Vitalian with mirrors of brass.
Moreover we are informed that Alexau.
der the Great provided the lighthouse of
Alexandria with mirror Of steel, by means
of which approaching hostile fleets could
not only be noticed when at a distance of
several hundred miles @, but that they
could also be set on fire when attempting
to besege the place. 1t is said to have
been afterwards destroyed by the Moham.
medans.
In the beginning Of the seventeenth cen.
tury, Father Kirchcr tried to prove expe-
rimentalIy that these stories were true.
Arranging plain mirrors in a curve, he
convinced himself that the reflected rays
of the sun will meet in one and the same
point or nearly so. "With five mirrors"
he says, I" could obtain great intensity
of heat at distance of one hundred feet
but what terrible phenomena would have
taken place had l used one thousand in
stead of five p
He ends by requesting his colleagues to
experiment in this direction with greater
care than they have been accustomed to
use. Still later, very effective burning
mirrors were constructed by Vlette and
Walther Won Tschirnhaqsen. Both made
them of metals. The Journal des Sauants
fhr 1879 gives an account of the fourth
and most perfect mirror constructed by
Viette. 1t was tbirty-four inches in di.
amcter, aud vitrifed flints and bricks
almost instantaneously when placed in its
fncus. Steel was converted into brilliant
sparks, of which some formed stars as
large as franc piece. Besides metals,
other materials were used for the construc.
,ion of burning mirrors. Gartuer, in
Dresden. fused asbestos with mirror of
wood gilled inside. Naumann, in 1899.
melted metals ia the focus of a mirror of
paste board, lined with straw; and the
royal Fcrdipand was presented with one Of
ice.
An illustration before US exhibits one of
the burning mirrors with which Button, in
1917, performed many extraordinary ex.
periments in the Jardin des Plantss, at
Paris. 1t was constructed of large nun,
ber of plane glasses, 6xS inches in size.
On the 3D. of April, at 2 o'clock in the
afternoon, the cr,at mirror was mounted
on its stand, and with its 12S glasses was
found to be capable Of igniting plank Of
wood ut a distance Of 1873 feet, although
the sun was covered with a mist during
the experiment. On the 5th of April, at
8 in the afternoon, with no better light,
they succeeded with 154 glasses 10 ignit-
ing at distance Of $50 feet, heap of
shavings of deal, mixed charcoal and sui.
phur. in less than minute and half.
When. however, the sun shone with its
full power. few seconds were sufficient
to accomplish these results.
On the 10th a pitched plank was easily
set on fire with 128 glasses, at distance
Of $50 feet. On the 1lth the focus xas
fixed at twenty feet from the mirror, and
combustible substances were ignited With
but twelve glasses, With FL glasses,
piece Of half burnt elm plank was set on
fire. and With forty-fve facets, piece Of
tin weighing 6 pounds was almost instau.
tancously fused. Sheet silver was fused,
and an iron plate was rendered red hot
with III glasses. When used at dis
tauce the focus was 6 to 7 inches 10 diam.
eter. Metals were sometimes dissipated
10 brilliant vapor, which was SO thick as to
cast shadow on the ground.
All the experiments related above can
also be performed with concave lens.
That the ancients we're 10 possession Of
such glasses becomes evident from pas
sage in Pliny's Natural History. Before
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