194 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
position, in contempt of all the laws which govern statical equilib- 
rium. 
The experimental study of spinning tops is carried on by very 
small boys and a few more or less aged people. Somehow, but I 
think quite wrongly, a top is regarded as a toy suitable only for a 
child, and that kind of amusement is scarcely encouraged by the 
benevolent despots who so completely direct the games of boys at 
school. Among older boys there used to be a regular game in Scot- 
land of ‘‘peeries,”’ and some of you may have read Clerk Maxwell’s 
poetical description of the Homeric contests which distinguished the 
sport. 
The top as a plaything is despised; nevertheless it is a most im- 
portant contrivance. The earth on which we live is a top, and a 
considerable range of astronomical phenomena are most easily 
explained by reference to the behavior of ordinary spinning tops. It 
is a top that directs the dirigible torpedo, that controls the monorail 
car, which may soon rise from the position of a small model to that of 
an important affair of practical railway engineering, and that in the 
gyrostatic compass gives a direction-pointer unaffected by the iron of 
the ship or the rolling and pitching of the vessel. Its properties 
(summed up in what we call gyrostatic action) have to be reckoned 
with in all swift-running machinery, such as fast-speed turbines and 
rotary engines of all kinds, especially if these drive flywheels or pro- 
pellers. They affect very seriously the stability of aeroplanes and 
even of submarines, and I am very doubtful if aviators have yet 
become in sufficient degree instinctively alive to the dangers of - 
sudden turning, such as those which are or used to be encouraged 
by the promoters of aviation displays in alighting competitions. 
The man who has spun and studied tops and gyrostats appreciates 
as no one else can the extreme importance of properly balancing 
rotating machinery, and of avoiding gyrostatic action where such 
action is likely to interfere with the running of the machine as a 
whole. 
The properties of a top are best studied in the gyroscope, or gyro- 
stat, as it is better called. Here is a simple gyrostat, of the ordinary 
form sold in the toy shops, but with some important modifications 
to enable it to run for a long time at a high speed. It consists, as you 
see, of a heavy-rimmed metal disk or flywheel capable of rotation 
with but little resistance from friction on pivots held in sockets 
attached to a metal frame. Thus the flywheel may, by the quick 
withdrawal of a string wound round its axle, or in some other way, be 
set into rapid rotation in the frame, which in turn is mounted in 
various ways to show gyrostatic effects. But this ordinary form, as 
well as some others of a more pretentious character, suffers from the 
