Observations on Visible Vibration. 



17 



107. The glass being clean and dry, and the powder 

 also well dried, the external surface of the glass was covered 

 with the powder by means of a fine sieve, the distribution 

 being made equal all over the surface by giving the foot of 

 the glass one or two gentle taps to get rid of accumula- 

 tions in particular parts; the bow was then applied to 

 the edge with the precaution of touching the glass at one 

 and the same spot in all the oscillatory movements of the 

 bow, and with an uniform pressure, so as to produce one 

 note only ; and in the first instance this note was the funda- 

 mental note E, first glass before mentioned. 



108. When the glass began to vibrate, some of the hea- 

 vier particles of the powder fell down from the external 

 surface, but the lighter particles were, as we at first sup- 

 posed, shaken from the surface, carried upwards, and hover- 

 ing like a slight cloud over the vessel, fell into it and 

 produced a regular quadripartite system on the inclined 

 interior side of the vessel, the powder being collected up 

 the nodal lines and an empty channel at the middle of each 

 vibrating sector as in figure 7. This, however, is not the 

 explanation of the eff'ect as I shall presently shew. 



Fis:. 7. 



109. The above figure was produced by the glass vibrat- 

 ing the note E, with the higher note B ; the result was the 

 formation of six distinct trains down the interior, each 

 train being narrower than in the former instance, and more 

 clearly separated from the intermediate spaces. The trains 

 did not approach so near the apex as in the former in- 

 stance. 



The second glass yielded similar results ; the lowest note 

 affording four trains, and the higher note E flat eight trains, 



VOL. IV. c 



