300 The American Geologist. May, isao 
Avill endeavor to show in how far these physical phenomena can 
be accounted for by mere structural differences and modifica- 
tions in the way of molecuhir grouping. 
There is no necessity that our particles should be primary 
in the sense of modern dynamics and chemistry, where an 
atom is defined as the smallest particle of an elementary sub- 
stance which by mere juxtaposition with the particles of other 
substances give rise to a combination, and where the term 
"molecule" is applied to the smallest conceivable aggregate of 
atoms in a compound body. 
An atom is, of course, practically invisible, and even the 
most complicated aggregate of atoms, as presented in the mole- 
cules of certain hydro-carbons, has hitherto escaped the resolv- 
ing power of ourbestlenses. But the particles of which Crystals 
are composed^ can be clearly discerned with a yL inch objective 
— very rarely in the finished crystal, but whenever a substance 
is examined under the microscope during the process of crys- 
tallization — and wherever the operation of crystalline forces 
can be observed under high powers of magnification. There 
are grounds for believing that each of these visible particles 
(of which more anon) is an augmented molecule, viz., an ag- 
greijate of molecules, just as a molecule is an aggregate of atoms 
and that no single molecule is capable of manifesting polar 
forces of sufficient energy to enable it to play a part in crys- 
talline economy. 
In reference to primary molecules and atoms it is obvious 
that all observations on their shape and dimensions must re- 
main speculative till opticians can furnish us with a combina- 
tion of lenses which affords an amplification of at least 30,- 
000 diameters. Considering the fact that no perceptible pro- 
gress has been made during the last twenty-five years in the 
efficiency of high power objectives'* — notwithstanding the per- 
*The high-power objectives made twenty-five years ago by A. Ross, 
Wenham, Powell & Lealand, Richard Beck and others have not been 
surpassed and are barely equaled by those of the most renowned mak- 
ers of the present. There has been absolutely no gain in amplifica- 
tion and the only apparent '"progress" made is the very doubtful one 
that we can now, at extortionate prices, purchase objectives of wide 
angular aperture and comparatively low magnifying power. The use 
of wide angled high-power objectives is limited to a few objects, and 
in powers lower than a ^ great angular aperture is an unmitigated 
nuisance. To desire wide angular aperture in a "half-inch" ob- 
jective is the hight of absurdity and it is to be regretted, in the interest 
of microscopy, that our opticians have been encouraged in the produc- 
tion of such monstrosities by a few addle-headed excentrics. 
