en powder and thorium oxide through a perforated diamond of the
desired diameter. The filament so produced is drawn through a chamber
heated to 2500 deg. C. at a velocity of eight feet an hour, which
crystallizes the tungsten into a continuous thread.

The first metallic filament used in the electric light on a commercial
scale was made of tantalum, the metal of Tantalus. In the period
1905-1911 over 100,000,000 tantalus lamps were sold, but tungsten
displaced them as soon as that metal could be drawn into wire.

A recent rival of tungsten both as a filament for lamps and hardener for
steel is molybdenum. One pound of this metal will impart more resiliency
to steel than three or four pounds of tungsten. The molybdenum steel,
because it does not easily crack, is said to be serviceable for
armor-piercing shells, gun linings, air-plane struts, automobile axles
and propeller shafts. In combination with its rival as a
tungsten-molybdenum alloy it is capable of taking the place of the
intolerably expensive platinum, for it resists corrosion when used for
spark plugs and tooth plugs. European steel men have taken to molybdenum
more than Americans. The salts of this metal can be used in dyeing and
photography.

Calcium, magnesium and aluminum, common enough in their compounds, have
only come into use as metals since the invention of the electric
furnace. Now the photographer uses magnesium powder for his flashlight
when he wants to take a picture of his friends inside the house, and the
aviator uses it when he wants to take a picture of his enemies on the
open field. The flares prepared by our Government for the war consist of
a sheet iron cylinder, four feet long and six inches thick, containing a
stick of magnesium attached to a tightly rolled silk parachute twenty
feet in diameter when expanded. The whole weighed 32 pounds. On being
dropped from the plane by pressing a button, the rush of air set
spinning a pinwheel at the bottom which ignited the magnesium stick and
detonated a charge of black powder sufficient to throw off the case and
release the parachute. The burning flare gave off a light of 320,000
candle power lasting for ten minutes as the parachute slowly descended.
This illuminated the ground on the darkest night sufficiently for the
airman to aim his bombs or to take photographs.

The addition of 5 or 10 per cent. of magnesium to aluminum gives an
alloy (magnalium) that is almost as light as aluminum and almos