Intelligence and Miscellaneous Articles. 123 



contain Stygina Murekisonce and other fossils found elsewhere in 

 Bala rocks. 



A description of new fossils forms the concluding portion of the 

 paper. 



X. Intelligence and Miscellaneous Articles. 



ON A ROTATIONAL MOTION OF THE KATHODE DISK IN THE 

 CROOKES TUBE. BY FRANCIS E. NIPHER. 



IT is well known that the equations which represent the pro- 

 perties of the magnetic held external to a conductor are incon- 

 sistent when applied to points within the body of the conductor. 

 Assuming the total magnetic force within to be tangent to a circle 

 whose centre is at the wire centre, and that the surfaces of equal 

 potential are radial planes. Assuming the force due to an element 



2 di 

 of the conductor of infinite length and of section ds to be —7-, it 



follows that the force at any point without the conductor varies 

 inversely, and at an internal point directly, as the distance from 

 the centre. If now within the wire we assume any radial plane 

 as a datum equipotential plane, and determine the locus of any 

 other equipotential surface, such that the difference of potential, 

 measured along the lines of force, is constant, this surface turns 

 out to be one having as a cross-section a spiral known as the lituus 

 having the radius as an external asymptote, and reaching the centre 

 after an infinite number of turns. It is evident that these internal 

 surfaces of equal potential cannot be both radial planes and spiral 

 cylinders. 



Maxwell disposes of this absurdity to which the equations lead 

 in the single sentence which closes section 606 of his ' Electricity 

 and Magnetism.' He says : " Within the substance of the con- 

 ductor, there is no such thing as magnetic potential." 



It has long seemed to me that this failure of the equations 

 must be the result of leaving some elements of the problem 

 out of the discussion. I have spent a great amount of time in 

 seeking for some rotational phenomenon hitherto unrepresented in 

 the equations. Until recently the results were wholly negative. 

 While recently experimenting with a Orookes tube I observed that 

 the circular aluminium disk of the kathode became slightly loose on 

 the aluminium wire, and that it was constantly rocking in rotarv 

 motion on the wire. After several days of use, during which it 

 had been decided to construct a tube with disks capable of rotation, 

 the kathode disk suddenly became loosened, and began to rotate 

 slowly on the wire as an axis. 



The bearings were somewhat rough, and the disk was not per- 

 fectly balanced. It often stopped, but then began to rock against 

 the obstacle until it again freed itself. The direction of rotation 

 was contrary to the hands of a clock, when the disk was viewed 



