420 
POPULAR SCIENCE REVIEW. 
silver were perfectly melted within twenty-five minutes from the period 
of lighting the gas in the cold furnace, and the metal was sufficiently hot 
to cast for rolling in twenty more minutes. A second quantity of 266 
ounces of the same metal was then introduced, and was perfectly melted 
in eleven minutes, with a consumption of 66 cubic feet of gas, value 
twopence — the price of gas being two shillings and eightpence per 1,000 
feet : in a further period of fifteen minutes the metal was sufficiently hot 
to cast for rolling. A quantity (116 ounces) of German silver was then 
introduced, and melted in fifteen minutes ; and after twenty-eight minutes’ 
longer heating, various highly-figured articles were cast in it, in a most 
perfect manner. The use of this furnace is extending rapidly, the smaller 
sizes being much used by dentists, jewellers, analytical chemists, assayers, 
enamellers, and others, in consequence of their readily fusing silver, gold, 
copper, glass, and even cast-iron, without the aid of a bellows or lofty 
chimney, by simply lighting the gas, and the crucible and its contents 
being at all times protected from the air, and yet perfectly accessible to 
examination, stirring, removal, &c. The burners of the larger-sized 
furnaces are formed of a series of plates of cast-iron, and may be readily 
removed from the furnaces and placed to heat a retort, muffle, reverbe- 
ratory chamber, or other apparatus where intense heat is required. It is 
intended to apply them to heating of steam-boilers and welding articles of 
wrought- iron. The safety of these furnaces, their regularity and self- 
supplying action, and perfect freedom from dust and smoke, render them 
advantageous in certain processes, such as enamelling, annealing, &c., 
where cleanliness and uniformity of heat are required. Their high degree 
of heat, without the aid of a blast, results from the very rapid and perfect 
mixture of the air and gas, and the combustion being consequently effected 
and concentrated in a very small space. 
Galileo's Weather-glass . — In the course of the year 1862 a letter appeared 
in the Athenaeum describing a very simple form of barometer, which was 
made by filling a pickle-bottle with water, and plunging into it a Florence- 
flask with the neck downwards. It was said that, before rain, the water 
rose two or three inches in the flask, and on the approach of fine weather 
it fell proportionately. These statements were then contradicted by other 
correspondents, who asserted that on the approach of fair weather the 
water rose, and as wet weather neared, it fell. Mr. George Rod well, 
F.C.S., now explains the origin of these contradictions. In experimenting 
upon the influence of the atmosphere on a water barometer of the kind 
described, he employed a tube with a diameter of of an inch, and a 
length of 2 feet 11 inches ; the bulb was 2 inches in diameter, and 
contained 68 cubic centimetres of air at 48° Fahrenheit. The open end 
being placed in a vessel of water, the latter fluid rose in the stem to a 
height of 12 inches. It was found that increased pressure of atmosphere 
and simultaneous diminution of temperature caused the water to ascend 
in the tube. This result took place for the following reasons: — (1) The 
tension of the outer air was greater than that of the air in the bulb. 
(2) The air in bulb was contracted by diminution of temperature. 
(3) The tension of the aqueous vapour in the bulb was diminished. It 
was found also that, for reasons of a converse nature, the water descended 
