34 , PHYSICS. . “ 
electricity produced in this way is called Galvanism,! or Voltaic? Electri-: 
city. When two plates, one of copper, and the other of zine rubbed 
over with mercury, are placed in contact in a vessel. of water in which is a 
little sulphuric acid, bubbles of gas are formed; and when the plates are 
removed, the zinc one is found to 
have i in weight, the part it has 
lost being dissolved in the water. The 
same action takes place, although 
the plates are not in contact, if they 
are joined by a copper wire, as 
in the figure. In consequence of 
this chemical action, it is found that 
a current of electricity passes along 
the wire from the copper plate, in 
which positive electricity is produced, 
to the zinc, in which negative is pro- 
duced. ‘Further, under the liquid, 
a current passes from the zinc plate 
to the copper; so that by means of 










tricity makes a complete circuit ; and 






name of a galvanic or voltaic circwit. 
By employing a number of plates, 

. . . . 
the zine ones being connected with 
the copper ones in a series, the strength of the current is of course 
increased, and such an arrangement is called a galvanic battery. 
For the proper understanding of what is to. 
description of magnets. There is a certain ore 
of iron which has the power of attracting iron. It 
was first found in Magnesia or Lydia, in Asia 
things) became changed into loadstone. When a 
small magnetic bar is nicely balanced on a fine 
point, it is called a magnetic needle, and has the remarkable property 
of always pointing north and south, being of course free to move.? Such 
a piece of ore is called a natural magnet. An artificial magnet can be 

1§o called from Galvani of Bologna, its discoverer. 
2 Voltaic Electricity, or Voltaism, so called from Volta, an Italian. 
3 The mariner’s compass consists simply of a needle of this kind, balanced in the centre ofa. 
circular box, on the edge of which are letters for the different points, N., S., E., W., &. 
the wire and the liquid, the elec- . 
such an arrangement receives the: 
follow, it will be necessary to give here a short. 
Minor; hence a piece of this ore was called a: 
Magnet, or Lydian-stone, which last name (prob-. 
ably from the power of the ore to lead or attract, 
