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Proceedings of the Royal Society of Edinburgh. [Sess. 
want that the gyrostat under description was contrived. It differs from the 
gyrostat already described in having the field magnet system external to 
the armature ring. Here, as before, the non-rotating mass is reduced to a 
minimum. The shaft is of great strength to permit of the gyrostat being 
jerked to and fro without danger of damaging the shaft. With this type 
of gyrostat the authors have succeeded in obtaining speeds of from 25,000 
to 30,000 revolutions per minute for considerable periods. 
It may be pointed out that the accessories are so designed as to admit 
of the motor-gyrostat being rapidly adapted to any particular experiment. 
The design of the gyrostat itself is simple, and the instrument may readily 
be taken to pieces and the parts quickly assembled again. In all, five 
motor-gyrostats have been in use throughout the present winter in the 
Natural Philosophy Department of the University of Glasgow, and have 
been the means of greatly stimulating the interest of the students of 
physics and engineering in rotational motion. It is the opinion of the 
authors that the education of an engineer is incomplete unless he has 
handled gyrostatic apparatus ; for experiments with such apparatus show, 
in a way that no other experiments can, the importance of carefully 
balancing rotating machinery, and of avoiding gyrostatic action of rotating 
parts where such action is a disadvantage. If the fact that we live on a 
top does not suffice to make top-spinning and gyrostatic action of universal 
interest, turbines and the rotating parts of other high-speed machinery 
make it an important subject for the engineer. For example, a turbine 
placed with its axis thwart-ship will, as the ship rolls, exert an alternating 
couple on the bearings in a plane parallel to that of the deck. If the axis 
of the turbine is fore and aft, such a couple has play as the ship pitches. In 
both cases a couple in a plane containing the axis and at right angles to 
the deck is called into play as the direction of the ship’s head is altered. 
In conclusion, the authors desire to express their deep thanks to 
Professor Gray for the lively and practical interest he has taken in the 
progress of the work described in the present paper. Rotational motion, 
spinning-tops, and gyrostatic action have always occupied a prominent 
position in the programme of dynamical subjects dealt with in the depart- 
ments of Natural Philosophy presided over by Professor Gray, and it is 
to this fact that the authors owe what knowledge they possess of the 
properties of rotating bodies. 
( Issued separately August 19, 1912.) 
