19 
ends of the tube having the opposite polarity to those of the 
bar. If this were all, however, this magnet would not have 
any advantage over the horse-shoe magnet, 
2. The close proximity of the tube to the bar enables the 
one pole to exert greater inductive action on the other, than 
in the case of the horse-shoe form. 
8. The electro-magnetic action of both sides of the coil is 
utilised in the same manner as in the astatic galvanometer. 
The current converts the tube into a magnet of opposite 
polarity to the bar, and hence these two magnets act upon 
each other by induction, which their relative positions 
enables them to do with the greatest effect. It appears 
from tlie researches of Dr, J oule that the larger the bar 
inside the coil the less will be the intensity of magnetism 
exerted in it by the coil. While it may be shown that the 
smaller the tube — the closer it is to the coil — the greater 
will be the intensity of magnetism excited in it. Also the 
inductive action of the iron in the tube on that of the bar is 
inversely proportional to the square of the distance between 
them. Hence it follows that the effect of using the outside 
as well as the inside of the coil must increase rapidly as the 
diameter of the bar approximates to the internal diameter of 
the tube. 
After the reading of the paper, Mr. h A ulkner exhibited 
some of his magnets ; and by means of iron filings scattered 
on sheets of paper produced some very beautiful diagrams 
illustrating the effect of the outside tube on the magnetic field. 
General Meeting, November 16th, 187 
llev. William Gaskell, M.A., Vice-President, in the Chair, 
Mi\ John Boyd, of Victoria Park, and Mr. E. W. NiXj 
M.A., of the Branch Bank of England, were elected Ordinary 
Members of the Society, 
