168 



New Mas'netic Electrical Machine. 



is made from a bar of two and one half inch iron, and fourteen 

 feet long. Its lifting power is about one thousand five hundred 

 pounds, and when the battery and armature are removed, it retains 

 a permanent lifting power of fifty pounds. Struck with this cu- 

 rious fact, I was led to the construction of the compound electro- 

 magnet. My first experiment was made with three separate lay- 

 ers of coiled wire round a wooden spool ten inches long, with a 

 bar of soft iron enclosed. This was connected v/ith two pairs of 

 plates and the spark and shock observed. The bar of iron was 

 then removed, and a bundle of annealed large iron wire, intro- 

 duced in its place. The sparks and shocks were increased to a 

 surprising degree. I then took a bundle of smedler wires four 

 inches long and wound them with only two layers of continuous 

 wire. The spark from this was as intense as that given by the 

 large bar in the spool. I next took seven pieces of good hoop 

 iron, well annealed, one inch wide, one fourteenth of an inch thick 

 and eight inches long. These were firmly rivetted together, and 

 the angles of the compound bar thus made, were rounded to pre- 

 vent cutting the wire. Four layers of coiled wire were then 

 wound upon it, and their ends attached to two connecting wires. 

 Nothing can be imagined more intense and beautiful than the 

 sparks produced by this little compound magnet. When a piece 

 of iron is burned with it, the ignited particles are frequently thrown 

 off, the distance of two feet, and occasionally fall to the floor. 

 For its size, it is the strongest electro-magnet I have ever known, 

 and when the battery is withdrawn, there is not magnetism 

 enough retained, to affect a very delicate needle. From this per- 

 fect neutralization of power, arises in great measure, the intensity 

 of the secondary current. The neutrality is partly due to the re- 

 duced size of the bars, but chiefly to the action of their similar 

 poles upon each other, when the exciting cause is withdrawn. 



Fig. 3, represents a small elec- 

 tro-magnetic bar, mounted for 

 rotation, with my pole changer 

 attached, v/hich is shown at a. 

 h b, are the conducting tangent 

 springs ; c c, mercury cups for 

 connexion with the battery. No 

 stationary magnets are here used, 

 the instrument being made with 



Fig. 3 



