Observations on Visible Vibration. 365 



result ; but if the glass be vibrated by passing the moist 

 finger round its edge so as to produce the fundamental 

 note, a system of four fans is produced, while the produc- 

 tion of the secondary tones does not disturb the surface of 

 the water ; it is, therefore, to be considered that the results 

 as stated in the present paper were obtained from glasses 

 vibrated at one point of the edge by means of a fiddle bow. 



97. In a passage from Dr. Young, already quoted, (10) it 

 is stated, " that a vibrating glass, or bell, divides in general 

 into four portions vibrating separately, and sometimes 

 into six or eight." When a glass is producing a tone, 

 whether fundamental or secondary, it must be considered 

 not that the tone is produced by the aggregate or sum of 

 four or more vibrating sectors, but that the same given 

 note is produced by each and every sector of the glass, so 

 that one part or sector would yield the note of the glass 

 even though the other parts or sectors were damped or 

 stopped altogether. If the sectors do not vibrate with 

 exact isochronism, interference will, of course, result, (12), 

 and it is to this nodal division that the peculiar softness, 

 combined with richness and delicacy of notes produced 

 from glass is probably due, for by it two purposes are 

 served : First, Four nodal divisions, or systems, vibrating 

 isochronously produce in every glass the fundamental tone ; 

 each division yielding the same note produces fullness and 

 richness, by the combined vibrations of the four sectors ; 

 and, Secondly, in addition to the fundamental tone, secon- 

 dary tones, amounting in large glasses to six or seven in 

 number, and in smaller glasses to three or four are ob- 

 tained, and the peculiarly high pitch of the upper secondary 

 tones, surpassing that of any musical instrument, may be 

 traced to nodal division, each secondary tone differing in 

 this respect from the nodal division of the fundamental 

 note, and without this difference secondary tones could not 

 exist. Some of the secondary tones that have been ob- 

 tained have been 6 or 7 octaves above the fundamental 

 note, and, in one case, as many as 8 octaves, when a glass 

 cylinder open at one end, 14 inches in length and 10 in 

 diameter, was employed, the fundamental note of which 

 resembled the lowest diapason stop of an organ. The 

 various tones, therefore, of a glass are clue to nodal division, 

 each tone offering a different nodal arrangement, and each 



