528 



Prof. D. E. Hughes. 



[Mar. 17, 



have a perfect zero : by turning the interior coil through any degree 

 we have a current proportional to this angle, and in the direction 

 in which it is turned. As this instrument obeys all the well-known 

 laws for galvanometers, the readings and evaluations are easy and 

 rapid. 



If the coil upon the stress bridge is perpendicular to the iron wire, 

 and if the sonometer coil is at zero, no currents or sounds in the tele- 

 phone will be perceived, but the slightest current in the iron wire 

 produced by torsion will at once be heard ; and by moving the sono- 

 meter coil in a direction corresponding to the current, a new zero will 

 be obtained, which will not only balance the force of the new current 

 but indicate its value. A perfect zero, however, will not be obtained 

 with the powerful currents obtained by the torsion of 2 milims. 

 diameter iron wire, we then require special arrangements of the sono- 

 meter which are too complicated to describe here. 



The rheotome is a clockwork, having a rapid revolving wheel which 

 gives interruptions of currents in fixed cadences in order to have equal 

 intervals of sound and silence. I employ four bichromate cells or 

 eight Daniell's elements, and they are joined through this rheotome 

 to the coil on the stress bridge, as I have already described. 



The magnetic properties of iron, steel, nickel, and cobalt, have been 

 so searchingly investigated by ancient as well as by modern scientific 

 authors, that there seems little left to be known as regards its molar 

 magnetism. I use the word molar here simply to distinguish or 

 separate the idea of a magnetic bar of iron or steel magnetised longi- 

 tudinally or transversely from the polarised molecules which are 

 supposed to produce its external magnetic effects. 



Molar magnetism, whilst having the power of inducing an electric 

 current in an adjacent wire, provided that either has motion, or the 

 magnet a change in its magnetic force, as shown by Faraday in 1832, 

 lias no power of inducing an electric current upon itself or its own 

 molar constituent, either by motion or change of its magnetic moment. 

 Molecular magnetism (the results of which, I believe, I have been the 

 first to obtain) has no, or a very feeble, power of inducing either 

 magnetism or an electric current in an adjacent wire, but it possesses 

 the remarkable power of strongly reacting upon its own molar wire, 

 inducing (comparatively with its length) powerful electric currents, 

 in a circuit of which this forms a part. 



In some cases, as will be shown, we may have both cases existing in 

 the same wire ; this occurs when the wire is under the influence of 

 stress, either external or internal ; it would have been most difficult to 

 separate these two, as it was in my experiments with the induction 

 balance, without the aid of my new method. 



Ampere's theory supposes a molecular magnetism or polarity, and 

 that molar magnetism would be produced when the molecular mag- 



