GYROSTATS AND GYROSTATIC ACTION.! 
By Prof. ANDREW Gray, M. A., LL. D., F. RB. 8. 
[With 10 plates.] 
We are accustomed in daily life to handle nonrotating bodies, 
and their dynamical properties excite little attention, though it 
can not be said that they are commonly understood. It is different, 
however, with rotating bodies. These, when handled, seem to be 
endowed with paradoxical, almost magical, properties. I have here 
an egg-shaped piece of wood. I place it on the table and it rests, as 
we expect it to do, with its long axis horizontal. Our experience 
tells us that this is the natural and correct position of the body. 
But I set it spinning rapidly on the table, as you see, with the long 
axis horizontal, and you observe that after an apparently wobbling 
motion it erects itself so that its long axis is vertical. It was started 
spinning about a shortest axis, but the body has of itself changed 
the spin, and it is now turning about the long axis. In taking this 
position it has actually raised itself against gravity through a height 
-equal to half the difference between the lengths of the long and 
short axes. This seems paradoxical, but the man who is in the habit 
of spinning tops knows that this is the proper position of the body; 
that it must stand up in this way when spinning rapidly on a rough 
horizontal plane. 
This experiment may be performed at the breakfast table with an 
egg as the spinning body. But the egg must be solid within—that 
is, it must be hard-boiled; a raw or soft-boiled egg will not spin. 
Perhaps this is why Columbus did not adopt this method for his 
celebrated experiment; there may, of course, have been other reasons. 
It is thus made clear that by causing a body to rotate rapidly we 
endow it with new and strange properties. Between a top when 
spinning and the same top when not spinning there is a difference 
which reminds us of that between living and dead matter; and this 
will strike us still more forcibly when we consider some more compli- 
cated cases of rotational motion. The top, the ordinary spinning 
top of the schoolboy, stands on its peg and ‘‘sleeps” in the upright 
1 Reprinted by permission from pamphlet copy published by the Royal Institution of Great Britain. 
Lecture at the Weekly Evening Meeting, Friday, Feb. 14, 1913. 
73176°—sm 1914 13 193 
