1886. ] Causes of Forest Rotation. 521 
direction of gravity, but not contrary to the direction in which 
that force is now working, which alone concerns us, 
The whole matter hinges on the ability of a plane to resolve 
the gravitating force as it resolves other forces. In doing so it 
does a very wonderful thing. It makes of gravity a continuous 
motive power. It introduces a new idea into our conceptions of 
things, and makes it imperative that we rectify our notions of the 
gravitating force so as to admit these facts, which we have not 
hitherto recognized. 
It dignifies the soaring birds into the position of favored crea- 
tures of nature. They inhabit a universe of their own. The 
horizon of their world is not the level of the sea, but the incline 
of their own wings, which they can change at will. Their gravi- 
tating force is either in a straight line from their bodies towards 
the center of the earth, or the moon, or the sun, or any of the 
stars of heaven, indifferently, as it suits them, to sleep on the 
breeze, to play at gymnastics high in air, to enact the rôle of the 
highway robber, or to serenely float from zone to zone. 
I have now presented the case of the soaring birds to the ex- 
tent of my ability. The task could have been better done by a 
Specialist in analytic mechanics, as it is in this sphere that its sig- 
nificance lies. The whole matter is extremely peculiar. In con- 
sequence of the throng of preconceived ideas which tend to cast 
the obscurity of night over the whole case, the evidence upon 
which it rests, although axiomatic throughout, is difficult to see. 
“ne mechanism also seems devoid of organization, a simple plane — 
is all there is of it,@na still it has the power to change the hori- 
zon of the world to suit its own purposes. It would be unwise — 
to suppose that a device capable of doing this was not competent - 
x give to man what he has long coveted, the power to navigate 
the air, A 
Certainly we must entertain two standards of horizontal, one 
the level of the sea, and the other the incline of the wings of the — a 
Soaring birds, Pil 
oo ` 
20. 
CAUSES OF FOREST ROTATION. 
att BY JOHN T. CAMPBELL. : Lees a 
P a letter recently received from Dr. S. V. Clevenger, he _— io 
| tioned a case coming under his own observation on the North J 
-CUS railroad, in Minnesota, near Mille Lacs, where the railroad 
