154 
POPULAR SCIENCE REVIEW. 
so we are not able to assign any limit to the minuteness which 
would be incompatible with the exercise of effective force. 
Becquerel has shown that when a membrane is moistened 
on each side by a different liquid, an electric wave force is 
set up, able to effect chemical decomposition. Thus the 
minutest part of the minutest gland, or of the smallest organism 
that is capable of assimilating external matter, is enabled to 
change the chemical condition, and pull asunder molecules or 
atoms that would resist the mechanical force of a steam-engine 
or a hydraulic press. 
Unfortunately, we have no chance of seeing the ultimate 
atoms or molecules of matter. Chemists use the term mole- 
cule to denote the smallest quantity of any substance capable of 
existing alone ; but the definition is not quite satisfactory, 
because they have reason to believe there are many compound 
molecules that only exist in parts of more complicated combina- 
tions. Could we, by help of any apparatus, see ultimate 
molecules, the sight would be an astounding one ; for an 
extremely minute portion of any substance, however solid 
and quiet it might appear to ordinary vision, would be 
exhibited to us as composed of infinitely more particles than 
all the stars we can perceive in a clear sky, and all in motions 
as harmonious as those of the celestial bodies. When either 
compositions or decompositions are going on we should see 
hosts, by the myriad, rushing together, or springing apart, as 
the case might be. Eternal motion is the condition of life, 
whether of the smallest unit or of the entire universe. Nature, 
as Humboldt said, is ever arranging herself in new forms, and 
absolute stillness would be cessation of being. 
The limits of visibility was one of the topics brought before 
the Royal Microscopical Society in February by the President, 
Mr. H. C. Sorby, in a remarkably able, and admirable, Annual 
Address. * Omitting the estimation of unavoidable errors in 
the construction of microscopical apparatus, and referring to 
researches by Pigott, Helmholtz, and Woodward, it seems that 
it is possible to distinguish the most favourable objects — 
alternate dark and bright lines such as in Nobert’s test-plates — 
when they are as near each other as to be only jy 2 1 000 of an inch 
apart, provided that several circumstances, which need not now 
be explained, are favourable. Minute spherules of about 
soiioo iocTooo an ma y a ^ so seen if their refractive 
power differs sufficiently from the fluid, or other medium in 
which they are immersed. It may, however, be affirmed that 
few objects less than — ^ of an inch in diameter can be seen; 
* See 11 Monthly Microscopical Journal,” for March 1876. 
