Ehrenberg has found from experiments on the dust of diamonds, that
a diamond superficies of 1/100th of a line in diameter presents a
much more vivid light to the naked eye than one of quicksilver of the
same diameter. On pressing small globules of quicksilver on a glass
micrometer, he easily obtained smaller globules of the 1/100th to the
1/2000th of a line in diameter. In the sunshine he could only discern
the reflection of light, and the existence of such globules as were
1/300th of a line in diameter, with the naked eye. Smaller ones did
not affect his eye; but he remarked that the actual bright part of the
globule did not amount to more than 1/900th of a line in diameter.
Spider threads of 1/2000th in diameter were still discernible from
their lustre. Ehrenberg concludes that there are in organic bodies
magnitudes capable of direct proof which are in diameter 1/100000 of a
line; and others, that can be indirectly proved, which may be less than
a six-millionth part of a Parisian line in diameter.