NATURAL PHILOSOPHY. 147 



through the same length of wire (1,125 miles), through which a single current 

 required a second and a half to discharge itself spontaneously upon the paper. 

 Having stated the precautions adopted to guard against error in the observa- 

 tions, the details of the experiments were then concisely given, including 

 those for "velocity," which showed a much higher rate attainable by the 

 magneto-electric than by the voltaic current. The author then recapitulated 

 the facts, to which he especially invited attention : First, the mode of testing 

 velocity by the use of a voltaic current divided into two parts (a split cur- 

 rent), one of which shall pass through a graduated resistance-tube of distilled 

 water, and a few feet only of wire, while the other part shah 1 be sent through 

 the long circuit, both being made to record themselves by adjacent styles 

 upon the same slip of electro-chemical paper. Second, the use of magneto- 

 electric "twin-currents," synchronous in their origin, but wholly distinct in 

 their metallic circuits, for the same purpose, whether they be made to record 

 themselves direct upon the paper, or to actuate relays or receiving instru- 

 ments which shall give contacts for a local printing battery. Third, the effect 

 of induction, retardation of the current, and charging of the wire, as shown 

 autographic-ally ; and contrasted with this fourth, the rapid and forcible dis- 

 charging of the wire by the use of an opposite current ; and hence fifth, the 

 use of this as a means of maintaining or restoring at pleasure the electric 

 equilibrium of the wire. Sixth, absolute neutralization of currents by too 

 rapid reversal. Seventh, comparison of working speed attainable in a given 

 length of wire by the use of repetitions of similar voltaic currents as con- 

 trasted with alternating magneto-electric currents, and which, at the lowest 

 estimate, seemed to be 7 or 8 to one in favor of the latter. Eighth, proof of 

 the co-existence of several waves of electric force of opposite character in a 

 wire of given length, of which each respectively will arrive at its destination 

 without interference. Xinth, the velocity, or rather amount of retardation, 

 greatly influenced by the energy of the current employed, other conditions 

 remaining the same. Tenth, no adequate advantages obtained in a 300 mile 

 length by doubling or trebling the mass of conducting metals. The author, 

 in conclusion stated his conviction that it appeared from these experiments, 

 as well as from trials which he had made with an instrument of the simplest 

 form, actuated by magneto-electric currents, that the working speed attainable 

 in a submarine wire of 1,125 miles was ample for commercial success. And 

 may we not, he added, fairly conclude also that India, Australia, and Amer- 

 ica, are accessible by telegraph without the use of wires larger than those 

 commonly employed in submarine cables? 



OX PERISTALTIC INDUCTION OP ELECTRIC CURRENTS IX SUB- 



MARINE TELEGRAPH-WIRES. 



The Mowing paper was read to the British Association by Professor Thom- 

 son. " Recent examinations of the propagation of electricity through wires in 

 subaqueous and subterranean telegraphic cables have led to the observation 

 of phenomena of induced electric currents, which are essentially different 

 from the phenomena (discovered by Faraday many years ago) of what has 



