Mr Barlow's Electro-Magnetic Experiments. $77 
the latter be held horizontally, and in a line with the centre of 
the former, this will continue to advance till the pole of the 
magnet is within the ring, and then proceed with considerable 
velocity till it reaches the middle of the magnet, where it re- 
mains perfectly stationary. If now the magnet be withdrawn, 
and changed end for end, and re-introduced into the ring, the 
latter will go off from the magnet, — turn itself round when quite 
free from it, — again advance, and settle itself as before in the 
centre. 
“ This very simple apparatus, which may be made at the ex- 
pense of about a shilling, throws great light upon the nature of 
the electro-magnetic action, and proves most satisfactorily that, 
notwithstanding the intimate relation between the electro-mag- 
netic and magnetic fluids, they are not identical ; for no pos- 
sible arrangement of simple magnets can be made that would 
lead one of them beyond the pole of another to find its state of 
equilibrium in the middle of the latter.'” 
66 Another form of this apparatus is shown in Fig. 11. 
“ Both ^the above apparatuses are much improved, by fixing 
to the cork a light glass-cylinder AB to contain the acid, instead 
of floating them in it ; the apparatus may then be floated on 
common water, and all the facts exhibited as above described. 
“ This appendage to the original construction is due to Mr 
James Marsh, already mentioned.'’ 
Fxp. IX. u To exhibit the action of the terrestrial magnetism 
upon a galvanic wire freely suspended. 
“ Let ABGD, Fig. 12. represent a rectangular piece of hard 
wood, having two grooves a b, cd, cut in it, parallel to its 
length, about half an inch in depth, which are to be filled with 
quicksilver for the experiment. C p, Z q, are wires fixed in the 
Board, and passing each into its respective groove, with cups for 
making the connection with the battery at Z and C. Dm is a 
long piece of silk proceeding from the ceiling, or some other 
convenient place, and to which is tied the wire kmn , bent as in 
the figure, the points k and n being slightly immersed in the 
quicksilver. If the connection be now made at Z and C with 
the zinc and copper sides of the battery, the moveable part 
kmn of the galvanic circuit, which has a great freedom of mo- 
