974 
Proceedings of the Royal Society 
connection between vibration and sensation. There are, too, some 
sweet substances having no relationship to an alcohol. We know, 
however, that one can get the same colour sensations from a solution 
of either a picrate or a chromate, two substances absolutely dis- 
similar in chemical properties ; the reason is, that they both give a 
group of vibrations in the same part of the solar spectrum. It 
would then be reasonable to expect that instances would be forth- 
coming of substances of dissimilar nature and chemical composition 
with similar tastes. It would seem probable, then, that there is a 
scale of vibrations which may stimulate the taste organs analogous 
to the visible spectrum. If a substance vibrates in a definite part of 
this scale, a definite taste will be produced. 
One must always remember that the tongue has, like the eye and 
unlike the ear, no power of analysis. It may be that just as a 
colour, say orange, may be produced by either a simple vibration, or 
a combination of vibrations, some higher and some lower in pitch 
than that of the simple one, so the same taste may, in like manner, 
be produced by a simple vibration or a compound one made up of 
simple vibrations of higher and lower pitch. 
In conclusion, it will be necessary to state very emphatically 
that it is analogy that this paper proves, — analogy in the produc- 
tion of the senses. It would be premature definitely to say how 
the vibrations of common salt produce irritation of the gustatory 
nerve. Is it by setting up a sympathetic vibration, as in the ear, 
where the sonorous waves set in motion the end-organs of the 
labyrinth ? Upon such a question I have no wish to hazard what 
could only be an opinion. In the eye vibrations stimulate the cones. 
How is this done ? It is quite conceivable that this is by setting up 
sympathetic vibrations, but many suppose it to be a chemical action. 
If we ask what is a chemical action, no adequate reply will be 
forthcoming, though many would hesitatingly affirm that even so- 
called chemical actions may have a vibratory and mechanical inter- 
pretation. When we say that we understand the manner in wdiicli 
the end-organs of the ear are stimulated, we mean that we can 
prove an analogy between the sympathetic vibration of a tuning 
fork, and of the organ of Corte, when effected by the same wave 
motion. This is nothing, however, but an analogy. The produc- 
tion, on the other hand, of end-organ irritation by light or molecular 
