I looked at the picture on p. 188 of Weir and Richards' book PHYSICS OF THE
ATOM to see the micrograph Glenn mentioned. The accompanying text says that it
was obtained using "an ingenious type of microscope employing both x-rays and
visible light". I have never heard of such a technique. If anyone else knows
what is involved, feel free to jump in.
However, what is clear from any kind of "picture" like this, whether it is
obtained using x-rays or scanning-tunneling microscopy (which is what Dave
referred to), is that it represents a "map" of the electron charge distribution
in the material being studied. The contrast in Glenn's black and white photo
reflects differences in electron density throughout the sample (in this case it
was a solid sample of FeS2). To someone who already accepts the modern view of
the atom as a positive nucleus surrounded by a negative charge distribution,
this is clearly evidence for the existence of atoms. To a determined
anti-atomist (like Comte), I'm sure this would not be regarded as conclusive
proof. A clever person could likely come up with an alternative explanation
for these results that does not involve the present-day atomic model of matter.
I certainly find the atomic view convincing, but these micrographs are only one
PART of a very extensive chain of evidence. I recommend Jean Perrin's book
(I think it is called The Atom, but I don't have a copy here) for an old but
thorough survey of this evidence.
Bottom line: I don't think any SINGLE piece of evidence is convincing...but
taken together they are quite persuasive.
Stan Zygmunt
Department of Physics and Astronomy
Valparaiso University