1878.] 
Suspended in Liquids. 
169 
to investigate. Leeuwenhoek was the most celebrated of 
the early microscopists, and appears to have frequently 
observed the motions of small bodies. 
One astonishing fadt about this subjedt is the small atten- 
tion paid to it in recent years. Microscopists have continu- 
ally had the phenomenon under their eyes, and it has often 
been mentioned as a mysterious one which might lead to 
great discoveries. Faraday’s attention was drawn to the 
matter by Brown’s tradts, and he gave a Friday evening 
discourse on the “ adtive molecules.” Part of the notes of 
this ledture have been published by Dr. Bence Jones, in his 
“Life of Faraday” (vol. i., p. 403) and are very interesting ; 
they end thus “ Lastly, the relation of these appearances to 
known or unknown causes. Analogy to other moving particles. 
Camphor. Supposed facility of explanation, not camphor 
motion. Takes place within pollen. Under water, inclosed 
by mica or oil — not crystalline particles — not attradtion or 
repulsion. Does not consist in receding and approaching — 
not evaporation answered as before — not currrents, too minute 
— oscillation — consider current in a drop — when currents, 
motion very different — not eledtricity of ordinary kind — • 
because do not come to rest, seen after hours — -so that the 
cause is at present undetermined. 
“ Mr. Brown supposed to be careless and bold, is used to 
microscopical investigations — has not yet been corrected— 
assisted by Dr. Wollaston — so that carelessness can hardly 
be charged. Then, what does Mr. Brown say ? Simply 
that he cannot account for the motions. 
“ Many think Mr. Brown has said things which he has 
not — but that is because subjedt connedts itself so readily 
with general molecular philosophy that all think he must 
have meant this or that — as to molecules, by no means un- 
derstand ultimate atoms — as to size, says that solid matter 
has a tendency to divide into particles about that size — • 
pulverisation and precipitation — if smaller, which may be, 
are very difficult to see — does not say that all particles are 
alike in their nature, but simply that organic and inorganic 
particles having motion — motion cannot be considered as 
distinctive of vitality — -connection with atomic or molecular 
philosophy.” 
It is plain that Faraday, although he correCtly puts aside 
many erroneous suggestions, could not explain the pheno- 
menon ; but it is strange that in his long life of indefatigable 
research he never recurred to the subjedt, nor did any other 
eminent physicist undertake the task. A few incidental 
remarks upon the subjedt are to be found in books on the 
