126 O. N. Rood—Optical method of studying the 
ART. X01 on an optical method, of studying the Vibrations of 
Solid Bodies ; by OaDEN N. Roop, Professor of Physics in 
Columbia College. 
of standard forks executing a known number of vibrations in 
is 
asecond. This me 
of Lissajous in point of exactitude, is, on the other hand, more 
easy of execution and more generally applicable to the study 
of the vibrations of solid bodies of very different forms. The 
nature of the method referred to will’ best be illustrated by a 
few examples. 
in the number of vibrations executed y them. in a second. 
For this purpose a short piece of fine steel wire is attached to 
each of the forks and they are supported in positions so that 
their vibrations shall be at right angles i 
to each other, as indicated in fig. 1. The : 
wires may have a diameter of one or two- 
tenths of a millimeter, or even less, and 
are to be attached with the least possible 
amount of soft wax or varnish. The 
bration and the intersection of the wires 
viewed against a bright background with 
a small telescope, it will be seen that an 
optical figure is developed, which is partly due to the same 
well known conditions that give rise to the figures of Lissajous, 
and partly to the circumstance that the wires move with less 
velocity when near their maximum deviation from the line of 
h 
rest. Hence, if the difference in phase - 3 
Is 0, an appearance like fic. 2 is pro- 
duced, which changes into fig. 3 when i Dy 
the difference in phase has increased to py Y 
indications of the same figures are shown in all cases, except 
__ when the difference in phase is one-fourth, three-fourths, &e., 
_ Of a vibration, or nearly so. This figure, then, is characteristic 
