4.  Until just a few years ago flying was popularly regarded as a
    dangerous hobby and comparatively few had faith in its
    practical purposes.  But the phenomenal evolutions of the
    aircraft industry during the war brought progress which would
    otherwise have required a span of years.  With the cessation
    of hostilities considerable attention has been diverted to
    the commercial uses of aircraft, which may conveniently be
    classified as mail-and passenger-service.

Men who first ventured the prediction that postal and express matter would one day be carried through the air were branded as dreamers.  Parts of that dream became a reality during 1918, and a more extensive aerial-mail program will be adopted this year.  The dispatch with which important communications and parcels are delivered between large cities has firmly established its need.

Large passenger-carrying aircraft are now receiving pronounced attention.  Lately developed by the Navy is a flying-boat having a wing area of 2,400 square feet, equipped with three Liberty motors and weighing 22,000 pounds with a full load.  It is the largest seaplane in the world, and on a recent test-trip from Virginia to New York carried fifty-one passengers.  At the present moment the public is awaiting the thrilling details of the first flight between Europe and America, which has just occurred as a result of the keen international rivalry involved between the various entrants.

The British are now constructing a super-triplane fitted with six 500 horse-power engines.  Originally intended to carry 10,000 pounds of bombs and a crew of eight over a distance of 1,200 miles, the converted machine is claimed to be able to carry approximately one hundred passengers.  It has a wing span of 141 feet and a fuselage length of 85 feet.

What about the power plants of the future aircraft?  Will the internal-combustion engine continue to reign supreme, or will increasing power demands of the huge planes to come lead to the development of suitable steam-engines?  Will the use of petroleum continue to be one of the triumphs of aviation, or will the time come when substitutes may be successfully utilized?

For aerial motive-power, the principal requirements are:  great power for weight with a fairly high factor of safety, compactness, reliability of operation under flying conditions, and safety from fire.  Bulk and weight of steam-driven equipment apparently impose severe restrictions upon its practical development for present aircraft purposes, but who is willing to classify its future use as an absurdity?

Steam operation in small model airplanes is no innovation.  Langley, in 1891-1895, built four model airplanes, one driven by carbonic-acid gas and three by steam-engines.  One of the steam-driven models weighed thirty pounds, and on one occasion