328 Mr Willis on the 



its lower edge, so as to place the plane of the leather at different 

 angles with that of the board, the following phenomena will be 



observed : 



If the leather be inclined to the board, as in Fig. 12, the current 

 will merely drive it outwards and fix it with its upper edge con- 

 cave to the board, as in Fig. 11, (which is a bird's-eye view of the 

 upper edge). 



If the leather be inclined from the board, as in Fig. 14, the 

 current will draw the upper edge inwards, maintaining it with 

 its upper edge convex to the board, as in Fig. 13. 



If, however, the leather be placed in the intermediate position 

 to these two, that is, parallel or nearly so to the board, the current 

 will excite and maintain strong vibrations in the upper edge of 

 the leather, producing a loud musical note, as long as the current 



is kept up. 



If for the board we substitute a similar frame with leather, 

 and apply the two frames opposite to each other, above the rect- 

 angular opening of the board, as in Figs. 16 and 18, we have an 

 arrangement somewhat resembling the glottis, in possessing a pair 

 of edges opposite to each other ; with this similar phenomena to 

 those just described are observable; namely, when the leathers 

 are inclined to each other, as in Fig. 16, the current maintains their 

 upper edges in the position Fig. 15. When they are inclined from 

 each other, as in Fig. 18, the current fixes them in the position 

 Fig. 17, but when nearly parallel puts them into strong vibration. 

 The angle at which they may be inclined to each other to make 

 vibrations possible varies with the tension of the leather and the 

 force of the current. For an examination of the reasons of these 

 phenomena I must refer to Note B ; it is sufficient for our present 

 purpose to know that it is not merely necessary for the vibration 



