Intelligence and Miscellaneous Articles. 393 
holes being about ;*,ths of an inch. On Icoking in at one of these 
holes you could thus sce through the tourmaline and the opposite 
hole, or, in other words, see quite through the bomb. An arrange- 
ment was also made by which part of the tourmaline might be viewed 
with the graphite behind it. 
The apparatus thus prepared was heated to a red or yellow heat 
in the fire, placed on a-brick in a dark room, and the tourmaline 
viewed by a polariscope which Mr. Gassiot kindly lent me. The 
following was the appearance of the experiment :— 
Without the polariscope the transparent parts of the tourmaline 
were slightly less radiant than the field around them. When the 
polariscope was used, the light from the transparent portions of the 
tourmaline was found to vary in intensity as the instrument was 
turned round. No change of intensity could be observed in the 
light radiated by the opake streaks of the tourmaline, or by the 
graphite. 
The light from the transparent portions was therefore partially 
polarized. The polariscope was then brought to its darkest position, 
and a light from behind allowed to pass through the tourmaline. 
The light was distinctly visible in this position, but by turning round 
the polariscope about 90° it became eclipsed. The mean of four 
sets of experiments made the difference between the position of dark- 
ness for the two cases 883°. It appears, therefore, that the light 
radiated by the tourmaline was partially polarized in a plane at nght 
angles to that which was transmitted by it. It was also ascertained 
that the light from the tourmaline which had the graphite behind it 
gave no trace of polarization. | 
LX. Intelligence and Miscellaneous Articles. 
ON THE MOTION OF THE STRINGS OF A VIOLIN. 
BY PROFESSOR H,. HELMHOLTZ, 
if HAVE been studying for some time the causes of the different 
qualities of sound ; and as I found that those differences depended 
principally upon the number and intensity of the harmonic sounds 
accompanying the fundamental one, I was obliged to investigate the 
forms of elastic vibrations performed by different sounding bodies. 
Among such vibrations, the form of which is not yet exactly known, 
the vibrations of strings excited by the bow of a violin are peculiarly 
interesting. ‘Th. Young describes them as very irregular ; but I sup- 
pose that his assertion relates only to the motions which remain after 
the impulse of the bow has ceased. At least, I myself found the 
motion very regular as long as the bow is applied near one end of the 
string, in the regular way commonly followed by players of the 
violin. I used a method of observing very similar to that of 
Lissajoux. Already, without the assistance of any instruments, one 
can see easily that a stiing moved by the bow vibrates in one plane 
only—the same plane in which the string itself and the hairs of 
