324 Proceedings of the Royal Society of Edinburgh. [Sess. 
of magnalium (cast in halves) fitted together over the motor, each half being 
provided with a flange at its outside to allow of the two halves being 
screwed together. 
In this type of motor-gyrostat the only rotating parts are this Gramme- 
ring armature, the commutator, and the two discs supporting the armature 
ring. The field magnet, the shaft, and the outside casing are stationary. 
The shaft projects slightly on both sides of the casing; each projecting part 
has a thread cut upon it to receive a knurled nut. The two nuts (these are 
not shown in the figure) are screwed against the outside casing, and thus 
fix the latter to the shaft. 
To keep the motor-gyrostat as cool as possible the outside casing is 
Fig. 2. — Parts of Motor- Gyrostat. 
pierced with a number of radial slots ; these are kept small so as to 
eliminate all danger of the fingers of an experimenter getting into contact 
with the rotating parts. 
Fig. 2 is a photograph of the various parts of the motor-gyrostat, and 
will render clear the construction of the instrument. 
It will be seen that this motor-gyrostat is designed to run on a con- 
tinuous-current circuit. It can be connected up to run as a series motor, 
or as a shunt motor, and may be wound to suit all voltages. In the motors 
constructed up to the present the total mass of each instrument is 6J 
pounds ; that of the rotating parts is 4 pounds. The diameter of the 
external case is 6J inches and the breadth is under 3 inches. It will 
thus be seen that the gyrostat is capable of being handled with ease and 
convenience. When going at full speed the rate of working in the motor 
is 100 volts. 
