290 
ON SMELL. 
perceiving tlie odour of bodies of slightly higher molecular weight 
than prussic acid. 
Let us now enquire what is the probable rate of such 
vibrations. Mr. Johnstone Stoney has made investigations of 
the ratio of the bright lines of some spectra, and has calculated 
their relations to each other. An analogy will make the nature 
of this relation more evident. When a note, say C below the 
treble clef, is sounded on a piano, not only the tone C is heard, 
but its octave C on the third space ; also G above the line ; 0 
on the third leger line ; E on the fourth ; G on the sixth ; B flat 
above the G ; and other notes. 
These are called harmonics or overtones. Now, if we knew 
these overtones, it would be possible to refer them to their funda- 
mental. So with light, the light evolved by incandescent gases 
consists of certain colours, which have each their own rate of 
vibration. 
Knowing these rates, it is possible to calculate the rate of 
vibration of the fundamental. This has been done by Mr. 
Stoney (Royal Irish Academy, Jan. 9th, 1871} with hydrogen 
with the following results : — 
Wave lengths, H, 4102*37 tenth seconds. 
F, 4862*11 „ 
C, 6563*93 „ 
These are the 32nd, 27th, and 20th harmonics of a fundamental, 
whose wave length is 0*1313 millimetre. The time of vibration 
is 4*4 fourteenth seconds. It may be objected that these 
coincidences are not a proof. But Mr. Stoney has measured the 
lines of the spectrum of chromy 1-chloride, and its 31 lines 
coincide with those calculated. 
The probability of the correctness of such a calculation 
approaches to almost absolute certainty. Now we have no 
means of recognising such fundamental vibrations, unless, in- 
deed, the sense of smell is our means of receiving them. 
