284 Chronicles of Science. [April, 



a magneto-electric machine, or any other rheomotor, into the coil of 

 the electro-magnet, in either direction ; and it will invariably be 

 found that the direction of the current, however powerful it may 

 eventually become, is in accordance with the polarity of the mag- 

 netism impressed on the iron core. 



A very remarkable increase of all the effects is observed when a 

 cross wire is placed so as to divert a great portion of the current 

 from the electro-magnet. The four inches of platinum wire, instead 

 of flashing into redness, and then disappearing, remain permanently 

 ignited. The inductorium, which before gave no spark, now gave 

 one half-an-inch in length. Water is more abundantly decom- 

 posed, and all the other effects are similarly increased. 



A certain amount of resistance in the cross wire is necessary to 

 produce the maximum effect. If the resistance be too small, the 

 electro-magnet does not acquire sufficient magnetism ; and if it be 

 too great, though the magnetism become stronger, the increase of 

 resistance more than counterbalances its effect. 



But the effects already described are far inferior to those 

 obtained by causing them to take place in the cross wire itself. 

 With the same application of force, 7 inches of platinum wire were 

 made red hot, and sparks were elicited in the inductorium .2% 

 inches in length. The force of two men was employed in these, as 

 well as in the other experiments. "When the interruptor of the 

 primary coil was fixed, ^the machine was much easier to move than 

 when it acted ; for when the interruptor acted at each moment of 

 interruption, the cross wire being, as it were, removed, the whole of 

 the current passed through the electro-magnet, and consequently a 

 greater amount of magnetic energy was excited, while at the inter- 

 vals during which the cross wire was complete the current passed 

 mainly through the primary coil. 



There is an evident analogy between the augmentation of the 

 power of a weak magnet, by means of an inductive action produced 

 by itself, and that accumulation of power shown in the static elec- 

 tric machines of Holtzman and others, which have recently excited 

 considerable attention, in which a very small quantity of electricity, 

 directly excited, is, by a series of inductive actions, augmented, so 

 as to equal, and even exceed, the effects of the most powerful 

 machines of the ordinary construction. 



The magnetic polarity of rifles is a subject to which Mr. Spiller, 

 of the Eoyal Arsenal, Woolwich, has lately drawn attention. He 

 finds that all the long Enfield barrels in the possession of the 

 volunteers of his company exhibit magnetic polarity, as the result 

 of the violent and repeated concussions attending their discharge, 

 in a direction parallel to r the magnetic meridian. The Eoyal 

 Arsenal range runs nearly north and south, and the rifles, when in 



