Observations on Visible Vibration. 367 



98. I have before stated, that the production of secondary 

 tones from glass vessels is acquired by practice, the modus 

 operandi being difficult to describe. I have, however, 

 lately observed a method which is not only easy of descrip- 

 tion, but also of operation, when the bow, and not the 

 moist finger, is the instrument employed for exciting vibra- 

 tion. When the glass is yielding, the fundamental tone 

 (the result of 4 nodal divisions), if the finger be pressed 

 upon a part of the periphery of the glass nearly opposite to 

 that whereon the bow is acting, the note will suddenly pass 

 to a secondary tone (the result of 6 or 8 divisions), and, by 

 applying two fingers, the other secondary tones can be 

 elicited. As soon as the desired secondary tone is pro- 

 duced, the finger, or fingers, should be removed ; for the 

 glass inclines to continue to vibrate the same note for every 

 stroke of the bow, provided a second stroke is taken before 

 the vibrations of the first have ceased. 



99. The conical glasses (two in number) before alluded 

 to, (95), were of the following dimensions : — Perpendicular 

 depth 3| inches, diameter at the mouth 4 inches. 



Besides these, several conical wine glasses of green glass, 

 and common chemical test glasses, were employed. Each 

 one always yielded one fundamental and two or more 

 secondary tones, both when empty and when filled about 

 two-thirds with water. 



The two largest glasses, which I shall designate, First 

 and Second, yielded the following results : — 



FIRST GLASS WHEN EMPTY. 



E middle octave of flute. Fundamental note, 



B third octave. ) •, 



„ , „ . > secondary tones. 



r sharp tourth octave. J 



Besides these, another secondary tone was produced, 



which, from its high pitch, I could not determine, but 



which I believe to be in the fifth octave. 



FIRST GLASS CONTAINING WATER. 



C sharp middle octave, } Fundamental note producing 



or second C of flute. \ 4 nodes as indicated by 4 fans. 



» i i.i • i A > Secondary tone. 



A sharp third octave. > _. , J 



y bix nodes. 



