208 Proceedings of Royal Society of Edinburgh, [may 2 , 
nothing has been advanced. Casual allusions to the probable or 
possible relationship between the tastes or smells of bodies and their 
chemical natures are sometimes though rarely found in the text-books 
of physiologists, but nothing more. While so much important work 
has been carried on during the last few years by Helmholtz, Preyer, 
Maxwell, Rayleigh, and others, in connection with both sound and 
sight, no one, until quite recently, has turned his attention to the 
investigation of either taste or smell. 
In a most interesting and suggestive article in Nature (June 22, 
1882), Prof. Ramsay brought forward many facts tending to demon- 
strate the dependence of smell upon the vibratory motion of odorous 
particles. He drew attention to the fact that many gases and 
vapours of low specific gravity — their molecules vibrating therefore 
with great rapidity — are perfectly odourless, and he saw in this an 
analogy to the rapid vibrations of the ultra-violet rays of the 
spectrum, and the rapid vibrations of an insect’s wing, both incapable 
of producing any impression on the eye and ear. He also described 
classes of substances alike in chemical and physical properties, such 
as the alcohols or fatty acids, as having generic smells ; the higher 
members of the groups producing sensations more powerful and 
characteristic than those of the lower ones. It will be my endeavour 
in the present paper to extend more fully this inquiry, and to de- 
monstrate by experimental methods the fact that smell, like sight 
and hearing, depends for its production on the vibrations of the 
stimulating medium, the quality of the sensation depending, in all 
cases, upon the kind of vibration which produces it. 
In a paper read before the British Association in 1885, and printed 
subsequently in the Proceedings of the Royal Society of Edinburgh 
(1886), I was able clearly to demonstrate these points for the sense 
of taste. That paper and the present one will be found to run on 
exactly parallel lines ; one is almost a recapitulation of the other, for 
what is true of taste is also true of smell. In order to avoid un- 
necessary recapitulation, I have touched lightly on many questions 
more fully discussed in the other paper, which should therefore be 
consulted. 
An investigation into the odorous properties of substances is to a 
certain extent limited, as many of them are without smell, especially 
those found in the inorganic world. In a description of odours one 
