174 A. M. Mayer— Researches in Acoustics. 
creases as their number per second increases, and in the case 
of the etherial vibrations we have analogical phenomena. In 
the acoustical experiment, if the fork be much out of tune with 
the pulses transmitted by the fiber, no motion is produced in 
the fork ; likewise, we may imagine that when the period of 
vibration of one or more of the constituent atoms of a certain 
molecule is far removed from unison with any of the etherial 
vibrations falling upon it, no motion, or chemical decomposi- 
tion, will ensue. 
The analogy between the two classes of phenomena is yet 
more striking when we remember that the fork selects, from the 
composite vibratory motion which traverses the fiber, only that 
ence. 
The following experiments show that the method of analysis 
we are now discussing surpasses in delicacy and sharpness 0 
definition any other method in which sympathetically vibrating 
bodies are employed. As already shown, the forks select from 
the composite vibratory motion which strikes them only those 
simple vibrations which are in unison with their own vibratory 
periods. This remark, however, requires some modification, 
though the qualification necessary is less than is required when 
other similar methods of analysis are used. In all cases of co- 
vibration there is a certain range of pitch, above and below the 
sound which is in unison with the existing vibration, through 
which the co-vibrating body responds. The farther the remove 
from unison the weaker the response.* But in some cases a 
to the membrane on the Ut, reed, and sounded the latter dur- 
ing a few seconds. After the reed was silent, I heard the fork 
