The Rev. N. J. Callan 07i a new Galvanic Battery. 477 



as often as the connexion oftlie lielix with the battery is bro- 

 ken. Now I have devised a small instrument by which com- 

 munication wilii the battery may be broken and renewed 3000 

 or 4000 times in a minute. Thus 3000 or 4000 shocks may 

 be received, and 3000 or 4000 electric currents of the highest 

 intensity may, in the space of one minute, be passed through 

 water, charcoal, metallic wires, or any other body. It should 

 be remembered that the voltaic current from the battery should 

 not be passed through more than 200 feet of the heliacal coil, 

 and that the shock should be taken from the whole length of 

 the helix. 



When a voltaic current passes through a very long wire 

 from a single pair of plates, the wire will give a shock at the 

 moment of breaking contact with the battery. I have found 

 that this as well as the shock from the electro-magnet in- 

 creases with the number of platrs. 



1 have made a great variety of experiments on electro- 

 magnets. My object in these experiments was to ascertain 

 four things: first, on what the quantity of attraction depends; 

 secondly, on what the distance at which that attraction is 

 exerted depends; thirdly, on what the shock depends; and 

 fourthly, whether by a voltaic current from a large battery, a 

 permanent magnet could be made, which would induce on soft 

 iron magnetism equal to that which is given to an electro- 

 magnet by a battery containing 20 large plates, or oOO four- 

 inch plates. In these experiments I employed three different 

 voltaic batteries, and electro-magnets of various forms. I used 

 the large battery already described; a small battery of 14 

 pairs of plates, in which each zinc plate was seven inches 

 square; and a Wollaston battery, containing 280 pairs of four- 

 inch plates. Some of my electro-magnets were straight, and 

 others of the horse-shoe form, and one was a square: the iron 

 bars varied in length from 20 inches to six feet, and in thick- 

 ness from two inches to half an inch. On one of these were 

 coiled 39 copper wires, on another four, on a third three, and 

 on others there was only one wire. 



From the results of these experiments, I have deduced the 

 following conclusions: First, that the quantity of attraction 

 increases with the length of the bar of soft iron, at least as 

 for as six feet, and with the thinness till it becomes about an inch : 

 and that it increases nearly in proportion to the number of 

 plates (when they are large) in the battery by which the electro- 

 magnet is magnetized. When the plates are only four inches 

 .scjuare the attraction increases, but slowly when the number 

 exceeds 100. Secondly, that the tlistance at which attraction 

 is exerted, increases also with the length and thickness of the 



