1835.] Observations on Visible Vibration. 435 



50. It is important and interesting to investigate the 

 changes undergone by a glass during vibration, in order to 

 obtain more information as to the multiform variety of 

 vibration in various bodies. I have obtained many curious 

 results, which I will detail hereafter. In the present paper, 

 I propose to state the effect of various fluids in modifying 

 or changing the note produced by the vibration of a foot 

 glass. 



51. It does not appear that performers on musical glasses 

 tuned by means of water have been aware that a fluid may 

 be added to a glass to a certain height without perceptibly 

 altering the note, or its capability of yielding sympathetically 



' the fundamental note, and that the quantity of fluid necessary 

 to modify or change the fundamental note depends upon its 

 specific gravity. Thus, for example, if a cylindrical foot 

 glass be taken, the fundamental note of which is the first 

 C in alt, and that note be sounded on a flute within one or 

 two feet, the glass will vibrate the same note though it 

 contain water to the depth of 1^ of an inch, and under. 

 If, however, that limit be passed, the fundamental note 

 begins to descend. 



52. The glass that I employed as a standard in the fol- 

 lowing experiments was 3 finches in height, omitting the 

 foot. I graduated it on the exterior side to twentieths of an 

 inch, and, in stating my results, I shall, for the sake of 

 convenience, adhere to the vicesimal division of the inch. 



53. By this it will be seen that there is a line passing round 

 the glass latitudinally , which line I propose to call the axis of 

 vibration, a point on which the fundamental note of the 

 glass seems to turn. There are other lines which I have 

 succeeded in tracing which will be described hereafter ; my 

 present purpose is with this one particular line. 



54. This line is probably fixed and invariable in the same 

 glass, but it appears to rise and fall in proportion to the 

 specific levity and gravity of the fluids employed. It is, I 

 believe, confined to the interior of the glass, for I incline to 

 think that active or positive vibration is confined to the 

 interior of a glass, the exterior being negative.* The 



* This, together with other changes undergone by a glass during vibration, 

 will form the subject of the next paper, wherein, the producing cause of the cur- 

 rents of mercury, and their action, will also be further considered. 



2f2 



