12S Construction of Galvanic Magnets. 



a certain extent, but not in proportion to the extension of the 

 surface. If we suppose a wire to be rolled out into a flat ribbon, 

 and covered with silk, we might suppose that the effect of the 

 wire would be increased directly in proportion as its surface be- 

 comes greater. If a wire j\ of an inch in diameter, be rolled 

 out to the width of half an inch, their surfaces will be as 3 to 12 

 nearly, and it might seem rational to suppose that the power of 

 the ribbon will be four times that of the wire, but this is not 

 found by experience, to be the case. The tenuity of the metal 

 opposes the free passage of the electric fluid, and the silk cover- 

 ing being thicker than the metallic ribbon, occupies too much 

 room, so that as many layers of the winding cannot be made in 

 the same space as of wire. Therefore, although the magnetic 

 energy of the ribbon is greater than of the wire, it does not 

 increase in the same ratio as the increase of the surface of the 

 winding. 



I have made many experiments with ribbons of fourteen oun- 

 ces copper, or of copper weighing fourteen ounces to the square 

 foot, of four ounces, and of two ounces copper, in all of which I 

 found that with the same weight of metal, the thinner the foil, 

 the greater the power of the magnet, but that with the same sur- 

 face, the ribbon from fourteen ounces copper, possessed much 

 more power than those from the lighter foils. 



I have repeatedly verefied a remark made by Dr. Page, in the 

 last number of this Journal, that those magnets which lift the 

 greatest weights, do not always answer best for rotating magnets. 

 The galvanic magnets constructed with metallic ribbon, although 

 they will lift more, with the same weight of copper than wire 

 wound magnets, yet they will not rotate with as much rapidity. 

 This I always supposed to be owing to the resistance of the air 

 as their bulk is greater, but from the experiments of Dr. Page, it 

 would appear that the whole eflfect is not to be attributed to this 

 cause, as the same discrepancy is observed among wire wound 

 magnets. It would hence appear evident, that galvanic magnets 

 constructed by winding soft iron with metallic ribbon, and espe- 

 cially compound magnets are best for stationary magnets, as they 

 lift the greatest weight, and consequently must have the greatest 

 attractive power ; but wire wound magnets are best for rotating. 

 Many experimenters also prove that the thinner the foil, the 

 shorter must be its length. A ribbon of fourteen or sixteen ounce 



