394 Intelligence and Miscellaneous Articles. 
the bow are situated. This plane was horizontal in my experi- 
ments. The string was powdered with starch, and strongly illumi- 
nated. . One of the little grains of starch, looking like a bright point, 
was observed by a vertical microscope, the object lens of which was 
fixed to one of the branches of a tuning-fork. ‘The fork, making 120 
vibrations in the second, was placed between the branches of a horse- 
shoe electro-magnet, which was magnetized by an interrupted electric 
current, the number of interruptions being itself_120 in the second. 
In that way the fork was kept vibrating for as long a time as I de- 
sired. The lens of the microscope vibrated in a direction parallel to 
the string, and therefore perpendicular to its vibrations. ‘The string 
I used was the second string of a violin, answering to the note A, 
tuned a little higher than common, to 480 vibrations, and therefore 
it performed four vibrations for every one of the tuning-fork. Look- 
ing through the microscope, I observed the grain of starch describing 
an illuminated curved line, the horizontal abscissze of which corre- 
sponded to thedeviations of the tuning-fork, and the vertical ordinates 
to the deviations of the string. I found it a matter of importance to 
use a violin of most perfect construction, and I was fortunate in get- 
ting a very fine instrument of Guadanini for these experiments. On 
the common instruments of inferior quality I could not keep the curve 
constante nough for numbering the little indentures which I shall 
describe afterwards, although the general character of the curve was 
the same on all the instruments I tried: the curve used to move by. 
jerks along the line of abscissze ; and every jerk was accompanied by- 
a scratching noise of the bow. On the contrary, with the Italian 
instrument, and after some practice, I got a curve completely qui- 
escent as long as the bow moved in one direction, the sound bere 
very pure and free from scratching. 
We may consider the motion of the string as being compen 
of two different sets of vibrations, the first of which is the principal 
motion as to magnitude. Its period is equal to the period of the 
fundamental sound of the string, and it is independent of the situation 
of the point where the bow is applied. The second motion produces 
only very smali indentures of the curve. Its period of vibration 
answers to one of the higher harmonics of the string. It is known 
that a string, when producing only one of its higher harmonics, is 
divided into several vibrating divisions of equal length, being sepa- 
rated by. quiescent points, which are called nodes. In all the nodes 
of the second motion of the string in the compound result at pre- 
sent considered, the principal motion appears alone; and also in the 
other points of the string the indentures corresponding to the second 
motion are easily obliterated, if the line of light is too broad. 
The principal motion of the string is such that every point of it 
goes to one side with a constant velocity, and returns to the other 
side with another constant velocity. 
PlateV. fig. 7 represents four such vibrations, corresponding to one _ 
vibration of the fork. The horizontal abscisse are proportional to the 
time, the vertical ordinates to the deviation of the vibrating point. 
Every vibration is formed on the curve by two straight lines. The 
