682 Professor Andrew Gray [Feb. 14, 



position, in contempt of all the laws which govern statical equili- 

 brium. 



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 Avrongly, 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 Uve is a top, and a 

 considerable range of astronomical phenomena are most easily 

 explained by reference to the behaviour 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 stabihty 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 turnings, such as those which are encouraged by the pro- 

 moters 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 toyshops, 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 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 rota- 

 tion 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 great disadvantage of 

 having no means of maintaining the sjiin, and the continual renewal 

 of the spin is a great nuisance. 



I have here a gyrostat (Fig. 1) in which this drawback has been 



