184 



Prof. D. E. Hughes. 



[May 10,. 



that they can, as [desired, be moved to any portion of the strip of iron,, 

 in order that different portions of the same strip may be tested under 

 a similar stress. 



The coil D is joined to a telephone J or a sensitive galvanometer, 

 whose terminals are reversed at each make and break of the current,, 

 and we may either pass the current in the manner described or may 

 reverse all the communications, passing the current through the coil 

 instead of the wire, and listening with the telephone to the induced 

 eurrent upon the iron wire alone. 



The phenomenon of molecular movement upon the passage of an 

 electric current through a wire or a coil surrounding a bar of iron 

 was discovered by Page, 1837, and De La Rive published several 

 memoirs on this subject in the " Comptes Rendus," 1846, wherein he 

 not only clearly demonstrates the molecular cause of the sounds 

 emitted at each change of the current, but also foreshadowed the 

 theory which he published later in his " Treatise on Electricity," 1853. 

 These movements have since been studied in a variety of ways, and 

 by different methods, but they are all based upon the discovery of Page - r 

 as these sounds accompany all the rotations produced by torsion, in 

 many cases too feeble to be heard, but becoming clearly audible by 

 means of the microphone. 



In my paper on " Molecular Magnetism," 1881, I proved by three 

 different methods the identity of these sounds with all the phe- 

 nomena of rotation. In the induction balance we observe only by the- 

 angular displacement of the molecules upon its wire or strip of iron,, 

 reacting both upon its own wire and the exterior coil ; and the 

 currents obtained from 1 centim. length of wire are sufficient to be 

 clearly heard in the telephone held 10 centims. distant from the ear, 

 and this with a feeble current of one Daniell element ; under these 

 conditions we hear no sounds in the wire itself, but they at once 

 become audible by increasing the electric current or by the use of the 

 microphone. We cannot, however, analyse sounds obtained in this 

 way, nor can we perfectly analyse the induced currents which 

 Matteucci was the first to obtain, unless we reduce them to a zero 

 by an induction balance, a zero from which it is perfectly easy to 

 perceive arid measure the slightest change in the molecular structure. 



Before relating a few of the representative experiments, and in 

 order to avoid repetition, I will repeat the theory I gave in my pre- 

 liminary note, based entirely upon researches on magnetism by the 

 aid of the induction balance. 



Theory of Magnetism. 



1. That each molecule of a piece of iron, steel, or other magnetic 

 metal is a separate and independent magnet, having its two poles 



