618 
Proceedings of the Royal Society 
pole split in two in the two prongs ; and another fork B, the two 
prongs of which are made like the poles of a horse-shoe magnet, 
with the handle an excrescence between, we find that while the 
fork A produces sounds alike with both prongs when held near the 
core, the two prongs of the fork B show a marked difference. The 
like pole to that of the core sounds much weaker than the other. 
All this is indicative of the ordinary magneto-electric induction at 
work. 
If we detach the coil from the magnet, we have still further 
illustrations of the same. Both forks, A and B, sound loudest when 
placed with one prong on its flat side over the hollow at the centre 
(fig. 1), and both continue to sound, but with diminished force, as 
they are withdrawn in the same position from the middle to the 
margin of the coil. When laid with the plane of the prongs hori- 
zontal (fig. 2), they act differently. The A fork has its best sound- 
ing position when each prong lies symmetrically to the hollow axis, 
and it has a position of silence at a point between the middle and 
the outside, whilst the B fork in these positions acts in the opposite 
way. There are two positions that the forks may occupy at the 
side of the coils, where their similar and dissimilar actions are 
again shown. The first is when the plane of the fork is perpendi- 
cular to the axis (fig. 3), where both forks transmit no sound when 
held in the middle of the coil, but are heard when vibrating on 
either side. The second is when the plane is parallel to the 
