er-cooled; 50 and 100 horse power;
weight 250 and 500 pounds.

E. N. V.--8-cylinder, water-cooled; from 30 to 80 horse power, according
to bore of cylinder; weight 150 to 400 pounds.

Curtiss--8-cylinder, water-cooled; 60 horse power; weight 300 pounds.

Average Weight Per Horse Power.

It will be noticed that the Gnome motor is unusually light, being about
three pounds to the horse power produced, as opposed to an average of 4
1/2 pounds per horse power in other makes. This result is secured by
the elimination of the fly-wheel, the engine itself revolving, thus
obtaining the same effect that would be produced by a fly-wheel. The
Farcot is even lighter, being considerably less than three pounds per
horse power, which is the nearest approach to the long-sought engine
equipment that will make possible a complete flying machine the total
weight of which will not exceed one pound per square foot of area.

How Lightness Is Secured.

Thus far foreign manufacturers are ahead of Americans in the production
of light-weight aerial motors, as is evidenced by the Gnome and Farcot
engines, both of which are of French make. Extreme lightness is made
possible by the use of fine, specially prepared steel for the cylinders,
thus permitting them to be much thinner than if ordinary forms of steel
were used. Another big saving in weight is made by substituting what are
known as "auto lubricating" alloys for bearings. These alloys are made
of a combination of aluminum and magnesium.

Still further gains are made in the use of alloy steel tubing instead of
solid rods, and also by the paring away of material wherever it can be
done without sacrificing strength. This plan, with the exclusive use of
the best grades of steel, regardless of cost, makes possible a marked
reduction in weight.

Multiplicity of Cylinders.

Strange as it may seem, multiplicity of cylinders does not always add
proportionate weight. Because a 4-cylinder motor weighs say 100 pounds,
it does not necessarily follow that an 8-cylinder equipment will weigh
200 pounds. The reason of this will be plain when it is understood
that many of the parts essential to a 4-cylinder motor will fill the
requirements of an 8-cylinder motor without enlargement or addition.

Neither does multiplying the cylinders always increase the horsepower
proportionately. If a 4-cylinder motor is rated at 25 horsepower it is
not safe to take it for granted that double the number of cylinders