410 



Mr. C. Brooke on the Nature [March 21, 



rotation of the mass is arrested the instant the magnet is excited; and 

 furthermore, if the mass be forcibly rotated, heat is developed in it. And 

 it has since been ascertained that if two cylindrical magnets be so placed 

 that their axes lie in the same straight line, their contrary poles being 

 opposed to each other, then, if a cylinder of copper be made to rotate on 

 its own axis, coinciding with the common axis of the magnets, no heat will 

 be evolved by its rotation. 



Now these phenomena must ahke be the necessary consequences of the 

 assumed dynamical theory ; for if the copper molecules be thrown into 

 spiral-wave motion, analogous to that of a pencil of circularly polarized 

 light, then the motion of all the disturbed particles will be one of revolu- 

 tion in planes to which the lines of magnetic force are normals : and the 

 inertia or energy of rotation (as it has been variously termed), the 

 resistance offered by each revolving particle to any change in the direction 

 of its axis of revolution (as exemplified by the gyroscope), will resist the 

 rotation of the mass in any direction perpendicular to that of the axes of 

 molecular revolution, and arrest its motion. And conversely, if the mass 

 be forcibly rotated in the above direction, or in any other direction at 

 right angles to the lines of magnetic force, heat will be freely developed, 

 doubtless by internal friction arising from the perpetual displacement of 

 the planes of molecular revolution. But in the second case, the axis of 

 rotation of the mass coincides in direction with those of the axes of 

 molecular revolution ; hence there is no displacement of the molecular 

 orbits, and consequently no internal friction, and very httle if any heat is 

 generated. 



The rotatory character of the magnetic wave is further confirmed by 

 the known fact that, if a plane-polarized beam pass through a transparent 

 solid in the direction of the lines of force of a powerful electro-magnet, the 

 plane of polarization will be rotated the instant that the magnet is excited. 

 The truth of a theory can be established only by the verification of its 

 necessary consequences ; and it may not be too much to assume that in 

 the present case the evidence already adduced by the writer is, in the 

 entire absence of all contradictory evidence, strongly presumptive of the 

 reality of the hypothesis. 



It has been authoritatively stated that ordinary electric and magnetic 

 waves cannot both be assumed to be spirals, because each of these forms 

 of energy notoriously evolves the other in a direction perpendicular to its 

 course ; and the question is not without grave dynamical difiSculties ; but 

 they may perhaps not be insuperable. It may possibly be that, from some 

 unknown constraining condition or property inherent in magnetic bodies, 

 a spiral wave, on being constrained into a spiral course, may lose its 

 original spirality, and become a secondary spiral, having molecular motion 

 in a direction perpendicular to that of the primary spiral. 



The relations between electric energy and some of its observed physical 

 results having thus been inferred, the question next arises as to the nature 



