on aeroplanes, we have yet to see just
what a court is going to say. It is easy enough for a manufacturer to
guarantee to build a machine of certain dimensions and according to
certain specifications, but when he inserts a clause in the contract to
the effect that the machine will raise itself from the surface of the
earth, defy the laws of gravity, and soar in the heavens at the will of
the aviator, he is to say the least contracting to perform a miracle.

"Until aeroplanes have been made and accepted as practical, no court
will force a manufacturer to turn out a machine guaranteed to fly. So
purchasers can well remember that if their machines refuse to fly they
have no redress against the maker, for he can always say, 'The industry
is still in its experimental stage.' In contracting for an engine no
builder will guarantee that the particular engine will successfully
operate the aeroplane. In fact he could never be forced to live up to
such an agreement, should he agree to a stipulation of that sort. The
best any engine maker will guarantee is to build an engine according to
specifications."

CHAPTER XX. SOARING FLIGHT.

By Octave Chanute.

[5] There is a wonderful performance daily exhibited in southern climes
and occasionally seen in northerly latitudes in summer, which has
never been thoroughly explained. It is the soaring or sailing flight
of certain varieties of large birds who transport themselves on rigid,
unflapping wings in any desired direction; who in winds of 6 to 20
miles per hour, circle, rise, advance, return and remain aloft for hours
without a beat of wing, save for getting under way or convenience in
various maneuvers. They appear to obtain from the wind alone all the
necessary energy, even to advancing dead against that wind. This feat is
so much opposed to our general ideas of physics that those who have
not seen it sometimes deny its actuality, and those who have only
occasionally witnessed it subsequently doubt the evidence of their own
eyes. Others, who have seen the exceptional performances, speculate on
various explanations, but the majority give it up as a sort of "negative
gravity."

Soaring Power of Birds.

The writer of this paper published in the "Aeronautical Annual" for 1896
and 1897 an article upon the sailing flight of birds, in which he gave
a list of the authors who had described such flight or had advanced
theories for its explanation, and he passed these in review. He a