1835.] Observations on Visible Vibration. 361 



the first glass ; the wire on the second will vibrate strongly, 

 and seek the nearest nodes and remain there. These two 

 nodes are of course exactly opposite to each other, and may 

 be marked with a dot of ink on the side of the glass imme- 

 diately below. The two other nodes are midway down, as 

 may be seen by moving the wire away from the two first 

 nodes, so as to be within the sphere of attraction (if I may 

 so speak) of the two second ; the wire will almost immedi- 

 ately attain those two points, and if the finger be slackened 

 in its pressure, so as to produce a clear but not a full note, 

 in order that the wire may not be jerked, and the finger be 

 then removed, the wire will invariably rest on the nodal 

 points.* 



1 1 . Various forms of wire may be adopted ; a half circle 

 terminated with loops or hooks ; or a right angle, the sides 

 of which simply rest against the glass, while the apex 

 points towards the bottom of the glass ; or what, perhaps, 

 is most striking and satisfactory of all, four curved pieces 

 of wire, resembling ladies' hair pins, only with very short 

 legs, maybe employed, one leg within and another without 

 the glass. On placing these midway between each of the 

 four nodes, and vibrating the unisonant glass, the wires will 

 find out the nodes and continue to vibrate there. 



12. I need not, of course, remark that the nodes are not 

 always, strictly speaking, at four equidistant points of the 

 same circle. One direction may contain more or less matter 

 than another, and when this is the case to an appreciable 

 extent, there will be an interruption in the vibration. For 

 instance : I find that in foot glasses, the rim of which is about 

 three inches in circumference, there are always four nodes which 

 are, or ought to be, equidistant ; if this be not the case, the 

 space between the first and second node will vibrate quicker 

 or slower than the space between the second and third, and 

 so on. Now, if one space vibrate 100, and another 101 

 times in a second, there will be an interference, and, conse- 

 quently, a momentary interval of silence. This may be 

 observed in a foot glass under the circumstances before 

 mentioned ; if the note be produced by the moistened finger, 



* I should observe, that if, when the wire is vibrating at the node, one end be 

 moved away a little from that point, it will instantaneously regain the node, as if 

 it were a metallic spring. 



