1868. | Physics. 113 
hold the pair of pictures, which may be an ordinary stereoscopic slide 
turned upside-down; 2, a sliding piece near the middle of the 
board, containing two lenses of six feet focus, placed side by 
side, with their centres about one inch and a quarter apart; 3, a 
frame, containing a large lens of about eight inches focal length, 
and three inches diameter. The observer stands with his eyes about 
two feet from the large lens. With his right eye he sees the real 
image of the left-hand picture formed by the left-hand lens in the 
air close to the large lens, and with the left eye he sees the real 
image of the other picture formed by the other lens in the same 
place. The united images look like a real object in the air, close to 
the larger lens. This image may be magnified or diminished at 
pleasure, by sliding the piece containing the two lenses nearer to or 
farther from the picture. 
Heat.—Herr CO. Sching has investigated the subject of fusible 
silicates, and the temperature required for forming and melting the 
same. He finds by application of a thermo-electric pyrometer that 
silicates are formed and melted at the same temperature, and that 
the formation of the silicates depends more on time than on tem- 
perature, z.e. it depends, in fact, on the conducting power of heat 
which the materials composing the silicates possess. He also finds 
the temperature required for melting metals and metallurgical pro- 
ducts to be lower than usually stated, 1,431—1,445°, for melting the 
same. Sching now finds that a temperature of a glass furnace in 
operation is only 1,100—1,250° C.; that crystal glass is worked at 
833°, and becomes completely liquid at 929°. A Bohemian green 
glass tube softens at 769°, and becomes liquid at 1,052°. Pure 
limestone loses its carbonic acid by heating for several hours at 
a temperature of 617—675°. An increase of the temperature will 
shorten the time. 
Mr. C. Tomlinson, F.R.S., in a communication to the ‘ Chemical 
News,’ has stated his opinion that the Camphor Storm-Glass is use- 
less as a meteorological instrument. The frequent reference made 
to it by the late Admiral Fitzroy gave an almost official sanction to 
its use, and induced some instrument makers to manufacture it 
largely, and even to attach it to the ordmary barometer and ther- 
mometer. This led Mr. Tomlinson to examine the storm-glass with 
some care. One was made on a large scale in a quart bottle, placed 
on the window ledge, and a journal of its behaviour kept during 
some months. The conclusion arrived at was that the storm-glass 
is not acted on by light, or atmospheric electricity, or wind, or rain, 
&c., but solely by variations in temperature ; that it is, in fact, a rude 
kind of thermoscope, vastly inferior to an ordinary thermometer, 
and has no meteorological value whatever. 
VOL, V. I 
