Experiments on Vibrating Surfaces. 393 



For example, when you fupport a and b (Jig, 3.), and rub 

 with the bow in c, fig, 7. alfomay be produced, becaufe thefe 

 figures have both thefe points at reft. To produce fig. 2. you 

 fupport with one finger the part e, and rub with the bow in c; 

 and in this manner fig. 7. cannot be produced, becaufe it has 

 not the point e at reft. One of the greateft difficulties in produ- 

 cing the figures is to determine before hand the vibrating and 

 refting points which belong to a certain figure and to no 

 other. 



Hence it happens that when one is not able to fupport 

 thofe points which diftinguifh one figure from another, if 

 the violin bow be rubbed againft the plate, feveral hollow 

 tones are heard without the fand forming itfelf as expected. 

 One muft therefore acquire by experience a readinefs in being 

 able to fearch out, among thefe tones, that which belongs to 

 the required figure, and to produce it on the plate by rubbing 

 the bow againft it. But it requires great practice to deter- 

 mine the figure previoufly from the tone, or to fearch out, 

 among various tones, that which belongs to the figure, and 

 to know how to make the plate vibrate in fuch a manner 

 that this tone alone, and not another, (hall be heard. For 

 this purpofe you muft firft liften, and then alter the mode of 

 rubbing ; and as foon as the right tone is produced, you muft 

 rub fomewhat harder with the violin bow, by prefling it more 

 ftrongly againft the edge of the plate. The latter muft be 

 done in particular in regard to high tones. As foon as you 

 have acquired fufficient expertnefs in this refpect, you can, 

 as I myfelf have experienced, determine before hand, with a 

 confiderable degree of certainty, the figures to be produced, 

 and even the moft difficult. This practice will be attended 

 with the greateft advantage, if, when you rub the bow againft 

 the plate for the firft time in order to produce a figure, you 

 continue the rubbing that the tone may be imprinted in the 

 memory, and if you try, after fome time, t® produce the fame 

 tone again. It may be readily conceived that you muft not 

 forget what parts of the plate, and in what manner you 



damped ; 



