Thomson Air Blast.
Reading edition
It consists of an elliptical box II whose sides have perforations II where air can enter while inside of this rotates a steel disk keyed to the armature shaft and having radial slots in which slide three wings RRR of ebonite which as they fly around drives air into the holes JJ leading to the nozzles Fig. 15. The result is that, since the spark is done away with, oil can be supplied to the commutator in limited quantities but still amply sufficient to reduce the wear on the commutator to such an extent that the life of a segment is greatly increased. The air blast is fastened to the dynamo frame just behind the commutator and can be see in Fig. 23.