Dr. Howard on Electric Radiation. 61 



tion is continued the sparks reappear and regain their former 

 brilliancy, when the resonator again reaches its first position. 

 If the resonator be placed in the axial plane and then moved 

 parallel to itself towards the edge of the lens, the intensity of 

 the sparking gradually decreases as we get nearer the edge, 

 and on the side nearest the wall the sparks cease altogether 

 at the edge of the lens. On the other side, however, they 

 are visible right up to the edge of the lens, and then very 

 abruptly cease, when the direct effect alone is obtained. The 

 beginning of the sparking, as soon as the resonator enters the 

 shadow of the lens, is very noticeable. The same appearances 

 are observed at all distances from the first lens, but the 

 intensity of the radiation is, of course, smaller as we get 

 further from the oscillator. The radiations are always a little 

 more feeble on the side nearest the wall than on the other 

 side. The cause of this has not yet been definitely ascer- 

 tained, but it appears to be produced by some action of the 

 wall itself. Slightly altering the position of the oscillator did 

 not get rid of the effect ; so it cannot be due to the oscillator 

 being out of focus. There was apparently no defect in the 

 lens itself which could account for it. The concentration of 

 the radiations by the lens is very "well marked. Just after 

 passing through the first lens in the axial plane they are 

 almost as intense as when they first impinge on its curved 

 surface; that is to say, they do not lose appreciably in intensity 

 by traversing the 21 centim. of pitch. But this concentra- 

 tion is even more clearly shown by the fact that in the axial 

 plane, at the surface of the second lens (250 centim. from the 

 oscillator), the sparks are quite as intense as the direct effect 

 would be at 100 centim. in the same plane if the first lens 

 were removed ; or, again, the resonator will give sparks 

 easily at the surface of the second lens, and when brought to 

 the line of reference will not give sparks at a greater distance 

 than 70 centim. At the surface of the second lens the 

 irregularity mentioned above is a little greater than at the 

 surface of the first one. 



Beyond the second lens the rays are converged, as we 

 expected, and there is a fairly well defined point in which 

 they meet ; but the intensity of the sparking at the focus of 

 the second lens is not appreciably greater than at its surface. 

 Probably this is due to the fact that the rays from the edge 

 of the lens, having travelled a much longer distance in air 

 than those in the axial plane, have thereby lost much of their 

 intensity ; and the differences between the intensities at 

 different points could only be detected by a resonator with 

 more delicate adjustments. The cone of rays between the 



