1835.] Observations on Visible Vibration. 363 



sound produced by the shot is of a peculiar kind ; their 

 vibration even continues for some seconds after the finger 

 is taken from the glass, in consequence of the momentum 

 they and the glass have acquired, and the note gradually 

 becomes more acute and faint. 



17. If a large glass be employed in the above experiment, 

 (15) and the finger be well moistened, and in its rotation 

 pressed rather heavily on the edge of the glass, so as to 

 produce a strong full noise, some of the shot will start from 

 the circumference to the centre, and there remain in a state 

 of rest. Indeed, the tendency of globular bodies is to the 

 centre, where they remain in a quiescent state. 



18. A totally different appearance can be communicated 

 to the surface of the mercury, by moving the finger, not in 

 continued order round the glass, but with a jerking kind 

 of motion, pressing heavily, and resting for a moment at 

 intervals of about an inch. The mercury is then thrown 

 into broad concentric circles, sometimes perfect and some- 

 times broken. 



19. The mercury can also be made to assume a variety of 

 forms, according to the mode of vibrating the glass, and 

 the quantity of mercury employed, by drawing a bow against 

 the edge or edges of the glass ; by pressing the finger more 

 or less heavily ; or by passing it round with greater or less 

 rapidity. 



20. When the mercury is very clear the edge of the glass 

 will be seen distinctly reflected in it ) if a large soda water 

 glass be employed, and the finger moved slowly round, the 

 reflected edge will be seen thrown into a series of nodes 

 and ventral segments. The forms are very various and 

 interesting, and depend on the circumstances just men- 

 tioned (19.) If the mercurial surface be covered with a 

 thin coating of oil, the edge may still be seen distinctly 

 reflected, but it is not disturbed during vibration. (23.) 



21. The glass below the mercury vibrates but little, nor 

 does the mercury vibrate much below its surface ; for the 

 hand can be placed round the inside of the glass below the 

 surface of the fluid, and the vibration of both seems unaf- 

 fected, except that the note does not sound so frill or so 

 clear. 



(22.) The same observation applies when gelatinous and 



