66 THE HAMILTON ASSOCIATION. 
by chemical decomposition, or is merely the conversion of chemical 
energy into electrical energy. The simplest of galvanic cell consists 
of a plate of carbon and a plate of zinc immersed in an exciting fluid, 
that is, some fluid containing an acid or some similar substance that 
will act upon one or both of these immersed elements. If the car- 
bon and zinc were equally acted upon there would be no current, 
but the zinc is easily acted upon by the acidulated water; chemical 
- decomposition takes place, the potential of the zinc is raised, and a 
- current of positive electricity starts at the zinc pole and flows towards 
and out of the carbon pole through any conducting medium that 
may join the elements together. 
The word Magnetism is named from the town Magnesia in 
Lydia, where an iron ore was found possessing remarkable attractive 
powers for iron. It is now applied to all the phenomena having a 
selective attraction for iron. We have three kinds of magnet: 1— 
The loadstone or natural magnet; 2--The piece of hardened steel 
which, when once magnetised, retains its magnetism and is called 
the permanent magnet ; 3—The electric magnet, of which I shall 
speak of later. By the invention of the mariner’s compass the fol- 
lowing scientific discoveries of capital importance are demonstrated : 
1—That the loadstone can transmit to iron with which it comes in 
contact a permanent property like its own ; 2—That a magnetized 
needle will, if suspended, freely assume a fixed position relative to 
the geographical meridian, a certain part of the needle turning 
always to the north and the part opposite to the south (the opposite 
parts are called the poles); 3—That like poles repel and unlike 
poles attract; 4—If a magnetized needle be broken into many 
pieces each piece is a miniature magnet with a north and south 
pole; 5—That every magnet has a space or field over which it acts, 
shown by the influence the magnet exerts upon the compass needle 
some distance from it; 6—That the geographical north pole and 
magnetic north pole are not identical, therefore the magnetic needle 
does not point due north and south, but a little to the east and 
west, according to the locality (this is called the declination or 
variation of the needle); 7—-That when a magnetized needle is 
balanced on a horizontal axis so that it can turn a vertical plane, it 
is found to set itself at an angle depending upon the locality with a 
north seeking pole pointing downwards if north of the equator, and 
