292 
ON SMELL. 
quality as a flute, although its harmonics are so high as to be 
beyond the range of the ear, so smells owe their quality to 
harmonics, which, if occurring alone, would be beyond the sense. 
It must be remembered that the harmonics are not heard 
separately from the fundamental, unless special means be 
adopted to render them audible, but they add their vibrations to 
those of the fundamental. 
When two sounds are heard simultaneously, they give a 
concord or a discord, but each may be separately distinguished 
by the ear. Tw^o colours, on the other hand, produce a single 
impression on the eye, and it is doubtful whether we can analyse 
them. But smell resembles sound, and not light, in this par- 
ticular. For in a mixture of smells, it is possible, by practice, 
to distinguish each ingredient, and, as I have shown, to match 
the sensation by a mixture. 
With regard to the mechanism by which smell is conveyed to 
the nerve, all that can be said is pure speculation. But as it is 
supposed that the vibrations of sound are conveyed to the 
auditory nerve through the small cirrhi, or hairs w^hich spring 
out of round cylindrical nerve-cells in the superficial layer of 
connective tissue of the spittilleum of the internal ear, and that 
each is attuned to some particular rate of vibrations, so it may 
be imagined that the hair-like processes connected with the 
spindle-shaped cells, themselves communicating with the nerve 
fibres of the olfactory nerve, are the recipients of the vibrations 
causing smell. Although the rate of such vibrations is ex- 
tremely rapid — no less, indeed, in the case of hydrogen, than 
44,000,000,000,000,000, or the four quadrillion four billionth 
part of a second — yet the wave-length is bj no means so small, 
for it averages the inch, a magnitude quite visible 
to the naked eye. And hydrogen has no smell ; those bodies which 
have smell, and higher molecular weight, must necessarily have 
a slower period of vibration, and possibly greater wave-length. 
