;w() 



sparks, a method described elsewhere in these Proceedings. A second is a 

 considerable increase in the two capacities, to obtain waves of greater inten- 

 sity. A third is a modification of the sound gap, or rather a disposition of 

 screens about the sound spark in order to obtain waves from the same spark 

 of both great and small intensity. These waves are photographed on 1 he -aim 

 plate, enabling one to determine their relative velocities. A few of tin results 

 are given in this preliminary paper. 



The details of the sound gap and screen are shown in Figure 31. A heavy 

 spark is passed between the platinum terminals P-P. This produces a 

 cylindrical sound wave shown in section at S, S. G is a cylindrical metal 

 screen, which I shall call a grating, concentric with the spark axis, and having 

 longitudinal slits or apertures 0, 0, cut in it, as shown in the figure, thus 

 forming a sort of grating. The grating is so placed that it intercepts but one 

 end, the left end in the figure, of the cylindrical wave, the right end or half 

 spreading out the same as if the grating were not in use. I shall call this wave 

 the main wave. Some of the energy of the left end of the wave is reflected by 

 the grating, but some of it passes through the apertures which thus become 

 sound sources, the waves spreading out in every direction from these sources. 

 I shall call these waves wavelets. 



