Observations on Visible Vibration. 13 



interior surface of the glass itself, and the dotted curves 

 without the circumference may be considered as indicating 

 the upward motion of the liquid waves against the sides of 

 the vessel, caused probably by the rebound of the liquid 

 after the first imj)ulse. The points of collapse of the two 

 systems of curves are the nodes where the liquid is not dis- 

 turbed during vibration ; thus the figure during vibration 

 represents four, six, or eight waves, with as many corres- 

 ponding troughs or hollows between every two waves. 



Fig. 3. 



This figure may also convey an idea of the six, eight, ten, 

 and twelve curved figures, all of which are very perfect of 

 their kind, and indicate correctly the divisions of a sonorous 

 vessel necessary to produce a note of a certain pitch. 



102. The perfection and beauty of the figures is much in- 

 creased, when, instead of a slight coating of lycopodium, a 

 thick one is applied to the surface of the water, so that the 

 upper surface be kept dry and free to move ; thus, figure 4 

 represents an effect of this kind where the outer dots as before 

 represent the vertical curves, and the surface exhibits a star 

 of four fans, composed of the dry powder ; these fans are 

 truncated within one-sixth of an inch of the glass, while 

 the semicircular spaces have only a thin adhesive coat. It 

 would appear that the first application of the bow throws 

 the dust up the glass where it remains, while the horizontal 

 figure is the result of many oscillatory movements of the 

 water, the distance of the truncated ends of the fans from 

 the glass remaining constant somewhere between a quarter 

 and one-sixth of an inch. In some cases by close inspec- 



