impossible to determine; but to me it does not appear as if the hawk did it from necessity. It has more the appearance of variation: just as you or I might walk fast at one moment and slowly at another, now this side of the street and now the other. A shifting of the plane of the wings would, however, in all probability, give some impetus: the question is, would it be sufficient? I have seen hawks go up in sunny and lovely weather—in fact, they seem to prefer still, calm weather; but, considering the height to which they attain, no one can positively assert that they do or do not utilize a current. If they do, they may be said to sail (a hawk's wings are technically his sails) round half the circle with the wind fair and behind, and then meet it the other half of the turn, using the impetus they have gained to surmount the breeze as they breast it. Granting this mechanical assistance, it still remains a wonderful feat, since the nicest adjustment must be necessary to get the impetus sufficient to carry the birds over the resistance. They do not drift, or very little.
My own impression is that a hawk can soar in a perfectly still atmosphere. If there is a wind he uses it; but it is quite as much an impediment as an aid. If there is no wind he goes up with the greater ease and to the greater height, and will of choice soar in a calm. The spectacle of a weight—for of course the hawk has an appreciable weight—apparently lifting itself in the face of gravitation and overcoming friction, is a very striking one. When an autumn leaf parts on still day from the twig, it often rotates and travels some distance from the tree, falling reluctantly and
