ABSTRACT
This chapter aims to prove by experiment that electromagnetic actions are propagated through air with finite velocity. The physics lecture-room in which the experiments were carried out is about 15 m long, 14 m wide and 6 m high. Parallel to the two longer walls there are two rows of iron pillars, each row of which behaves much like a solid wall with respect to the electromagnetic action, so that the parts of the room that lie outside these pillars cannot be taken into account. The action of the reflected waves can be quite well recognized between any one of the iron pillars referred and the primary oscillator; and similarly on the opposite side the electromagnetic shadow can be observed. In acoustics there is an experiment analogous to those last described, in which it is shown that when a tuning-fork is brought near a wall the sound is strengthened at certain distances and weakened at others.
