and Observations on Visible Vibration. 426 



128. Thus far I had proceeded with vessels with lips and 

 handles, when it occurred to me, that the very same pheno- 

 mena could be produced from glass goblets, provided one 

 portion of the rim of these vessels were damped. I, there- 

 fore, procured a damper (made of steel), which was screwed 

 firmly upon the upper part of the glass goblet, pressing 

 both surfaces, and the points of contact were covered with 

 leather. 



Upon vibrating the glass containing coloured water, I 

 obtained two fundamental notes : — two secondary tones of 

 the first kind, and two secondary tones of the second kind. 

 Thus, the analogy with the lipped vessels was complete. 

 I need only describe here the production of the two funda- 

 mental notes. 



If we take the whole rim of the glass, and call that part 

 to which the damper is fixed zero, the bow applied at 90°, 

 180°, and 270°, produces a note about a fifth lower than 

 the fundamental note of the glass without the damper, 

 because in this case, the damper is on a centre of vibration. 

 But if the bow be applied at 45°, 135°, 225°, and 315°, the 

 fundamental note of the glass is unchanged, because the 

 damper in such case, occupies the place of a node. 



When two or more dampers are employed, interesting 

 results are obtained, which will be stated hereafter, as they 

 do not belong to the immediate subject of this paper. 



129. A disk of glass 12 inches in diameter, and fixed in 

 its centre in a horizontal position had a damper screwed to 

 its edge. The surface of the plate was covered with a 

 layer of water, w^hich latter was retained on the disk by 

 means of a ridge of bees' wax passed round the disk a little 

 within its circumference.* This disk afforded two funda- 

 mental notes, and double secondary tones of the first and 

 second kinds. The results, then, as obtained from a glass 

 goblet with a damper, and a glass disk similarly furnished 

 are precisely the same, as when vessels with lips and handles 

 are employed. 



130. From what has been already stated, it will be seen 

 that it is easy to determine, previous to experiment, the 

 exact points on the periphery of a lipped vessel, or on a 



* In this way a disk of glass exhibits most of the phenomena of a goblet con- 

 taining water. Indeed, the disk may be^considered as a very shallow glass vessel. 



