Читать книгу Endless Amusement - Unknown - Страница 49

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 8½ 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; and the Time in Seconds, which they took in melting.	Weight in Grains.	Time in Seconds.
Pure gold	20	4
Pure silver	20	3
Pure copper	33	20
Pure platina	10	3
Nickel	16	3
A cube of bar-iron	10	12
A cube of cast-iron	10	3
A cube of 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