DE. miller’s EXETER LECTURE. 
337 
The curves produced by two notes sounded at the same 
moment may fit into each other at certain definite intervals. In 
such a case we have a harmonious combination; whereas, when 
the curves do not so fit, a discordant combination of sounds is 
the result. The annexed woodcut exhibits the curves produced 
by the notes of a common chord, the upper and lower curves 
representing those of the octave. The vibrations of a tuning- 
fork, or other sounding body, are transmitted to the ear through 
the air, which is thrown also into wavelike movements, the waves 
of sound being longer in the lower, and shorter in the shriller 
notes. In the treble C of the piano, which is produced by 512 
vibrations per second, the waves that it occasions in the air are 
2ft. long ; while in the C of the octave below, the number of 
vibrations is 256, or just half, and the length of the aerial wave 
is 4ft., or twice as great. 
The effects produced by vibration are not limited to those of 
sound. The still more remarkable phenomena of light and heat 
are connected with movements of this kind of intense rapidity, 
the frequency of which is so great as almost to baffle belief, 
from 35,000 to 70,000 such waves being contained in the space 
of a single inch in the case of light. 
It has been concluded from experiments, into a description of 
which time does not permit us to enter, that in all substances 
which give out light of their own — such as a piece of lime 
intensely heated in a jet of burning gas, or a rod of charcoal 
glowing in the extreme heat produced by a current of elec- 
tricity excited in a powerful voltaic battery, the particles of the 
solid are in a state of inconceivably rapid vibrati 9 n, and that 
these vibrations are transmitted to the eye by means of some 
infinitely subtle medium, termed the ether, which fills all space 
and the interstices of matter, and which, though not light itself, 
when thrown into vibration by a luminous object, excites in our 
eyes the sensation of light; just as the air, though not itself 
sound, yet, when thrown into vibration by a sounding body, 
excites in our ears the sensation of sound. 
I will now, by means of the voltaic battery, ignite a piece of 
charcoal very intensely. The light thus produced will occasion 
a series of intensely rapid vibrations in the portion of the ether 
contained in this room, and these will pass off in straight lines in 
