New Magnetic Elediical Machine. 167 



circuit is broken, a powerful secondary rushes in the same direc- 

 tion with the primitive battery current. Hence the bright spark 

 is occasioned by the passage of the secondary through the heated 

 air, occasioned by the combustion of the mercury. Now, if the 

 surface of the metal is covered with a non-conducting liquid, such 

 as oil, the circuit is broken with precision, while an obstacle is 

 offered to the consequent and secondary current, and the greater 

 part of it rushes through the body, or whatever conductor joins 

 the extremities of the coil. The apphcation of this fact is of 

 great value in the use of the magneto-electric machine. If a drop 

 of oil be put upon the break piece of the ingenious machine of 

 Clarke, its power will be greatly increased, while it preserves a 

 good contact by saving the metals from oxidation. I find also, 

 that if the stratum of oil be very thin, the spark is more brilliant 

 than without it, being partly due to the combustion of the oil. 

 The same is true also of charcoal points, when used with the de- 

 flagrator or magnetic electrical machine. It will be seen at once, 

 that the gain of power in this new magnetic electrical machine 

 must be very great. I notice in the last No. of this Journal, 

 that Clarke's machine has on one armature four thousand five 

 hundred feet of wire, whereas on one armature of this machine 

 there are only eight hundred feet. The source of this superior 

 action, is chiefly the use of the straight armature, instead of the 

 revolving horse-shoe. There is no advantage in covering a 

 horse-shoe (for electro-magnetic or magneto-electric purposes) 

 beyond the straight portion. Hence the piece of iron is longer 

 than necessary for the full and ready production, and neutraliza- 

 tion of the magnetic forces. The straight armature is covered 

 through its entire length, and covered with ease and precision in 

 a lathe. 



On a new compound electro-magnet, for the production of the 

 magnetic electrical spark, and also for attractive force. — The fol- 

 lowing positions, I think, may be considered as well established 

 by experiment. 1st. Yery long and large bars of soft iron, even 

 with a proportionate battery, acquire a comparative feebler mag- 

 netic intensity than smaller bars. 2d. That long and large bars 

 of soft iron, once charged by a battery, retain a greater degree of 

 magnetic power than smaller ones. The great magnet lately con- 

 structed by Dr. King of this city, (Boston) in imitation of Prof Cal- 

 lan's magnet, affords convincing proof of these facts. This magnet 



