Account Of The Wonderful Effects Of Two Immense Burning-glasses

Mr. de Tschirnhausen constructed a burning-glass, between three and
four feet in diameter, and whose focus was rendered more powerful by a
second one. This glass melted tiles, slates, pumice-stone, &c., in a
moment; pitch, and all resins, were melted even under water; the ashes
of vegetables, wood, and other matters, were converted into glass;
indeed, it either melted, calcined, or dissipated into smoke, every
thing applied to its focus.

Mr. Parker, of Fleet-street, made a burning-glass, three feet in
diameter; it was formed of flint glass, and when on its frame, exposed
a surface of 2 feet 8-1/2 inches to the solar rays. It had a small
glass fitted to it, to converge the rays, and heighten the effect. The
experiments made by it were more powerful and accurate than those
performed by any other glass. The following is a brief epitome of its
astonishing power.

--------------------------------------+-------+-------+
Substances melted, with their weight; Weight Time
and the Time in Seconds, which in in
they took in melting. Grains.Seconds
--------------------------------------+-------+-------+
Pure gold 20 4
---- silver 20 3
---- copper 33 20
---- platina 10 3
Nickel 16 3
A cube of bar-iron 10 12
--------- cast-iron 10 3
--------- steel 10 12
Scoria of wrought-iron 12 2
Kearsh 10 3
Cauk, or terra ponderosa 10 7
A topaz, or chrysolite 3 45
An oriental emerald 2 25
Crystal pebble 7 6
White agate 10 30
Oriental flint 10 30
Rough cornelian 10 75
Jasper 10 25
Onyx 10 20
Garnet 10 17
White rhomboidal spar 10 60
Zeolites 10 23
Rotten-stone 10 80
Common slate 10 2
Asbestos 10 10
Common lime-stone 10 55
Pumice-stone 10 24
Lava 10 7
Volcanic clay 10 60
Cornish moor-stone 10 60
--------------------------------------+-------+-------+

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