28 Lord Rayleigh on the Incidence of Aerial 



an instrument somewhat similar to the above, except that the 

 wire was of iron instead of nickel. 



In order to show that the current induced in the coil is at 

 any rate chiefly due to variations in the magnetization of the 

 nickel wire produced by the variations of stress, and not to 

 the relative motion of the nickel wire and the coil, the follow- 

 ing experiment was made : — A steel wire and a nickel wire 

 of the same dimensions were attached to similar wooden 

 diaphragms. These wires having been magnetized by stroking 

 them with a permanent magnet were in turn inserted into the 

 same solenoid and clamped as before at their lower ends. The 

 same watch telephone was used as a receiver with each. 

 The results obtained with the weakly magnetized nickel wire 

 were enormously better than those obtained with the strongly 

 magnetized steel wire. If the induced currents were chiefly 

 due to the relative motion of the coil and magnetized wire 

 the best results would have been obtained with the strongly 

 magnetized steel wire, since it can hardly be supposed that 

 the relative motions of the coil and magnetized wire differed 

 so much in the two cases as to cause such an enormous 

 difference in the results. 



V. On the Incidence of Aerial and Electric Waves upon Small 

 Obstacles in the form of Ellipsoids or Elliptic Cylinders, 

 and on the Passage of Electric Waves through a circular 

 Aperture in a Conducting Screen. By Lord Rayleigh, 

 F.R.S* 



THE present paper may be regarded as a development of 

 previous researches by the author upon allied subjects. 

 When the character of the obstacle differs only innnitesimally 

 from that of the surrounding medium, a solution may be 

 obtained independently of the size and the form which it 

 presents. But when this limitation is disregarded, when, for 

 example, in the case of aerial vibrations the obstacle is of 

 arbitrary compressibility and density, or in the case of electric 

 vibrations when the dielectric constant and the permeability 

 are arbitrary, the solutions hitherto given are confined to the 

 case of small spheres, or circular cylinders. In the present 

 investigation extension is made to ellipsoids, including flat 

 circular disks and thin blades. 



The results arrived at are limiting values, strictly applicable 

 only when the dimensions of the obstacles are infinitesimal, 



* Communicated by the Author. 



