518 The American Naturalist. [June, 
some reasons opposed to this view mentioned by Dr. Hensoldt in 
an interesting article on Crystallogenesis (Am. Geologist, May 
and June, 1890). If we could magnify objects 30,000 diameters, 
and not thereby reduce the illumination too much, we might see 
a single molecule. At present the limits thus far reached are 
some 1600 diameters. “ But,” Dr. Hensoldt says, “the particles of 
which crystals are composed can be clearly discerned with a 7s inch 
objective,—very rarely in the finished crystal, but whenever a sub- 
stance is examined under the microscope during the process of 
crystallization, and wherever the operation of crystalline forces 
can be observed under high powers of magnification. There are 
reasons for believing that each of these visible particles is an ag- 
gregate 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 crystalline econ- 
omy.. . ‘The angular hypothesis’ which maintains that the fun- 
damental force of a crystal is determined by the shape of its 
integral molecules, has very few adherents now. . . On the other 
hand, the spheroidal form of the planets, the tendency of fluids to 
assume the spherical shape and the mechanical facilities which the 
hypothesis of rounded particles offers in the grouping of mole- 
cules have induced later inquirers to adopt almost unanimously 
the views of Wollaston and Hooke. We are now in position to 
show. . . that molecules must be more or less spherical, and in the 
case of augmented molecules,. . . or the minutest parts of which 
crystals are composed, we have abundant direct proof of this, as 
their forms are revealed to us by a magnification of less than 1 500 
diameters,” 
Dana continues: “(2) The living being enlarges by means of 
imbibed nutriment through a process of evolution ; and not by 
mere accretion or crystallization.” 
is use of “ evolution” is vague, and an enlargement by other 
object, and that is by adding matter to it or by stretching further 
apart the particles of matter which it already has. 
