98 Rk. J. ANDERSON [aAveusT 
a few, and at last even to these. Yet even a superficial study of such 
figures and forms must lead one on to the consideration of the forces 
at work. There is exhibited on approaching the living form a remark- 
able feature which living things possess beyond inorganic forms, viz. the 
greater power and facilities which a living organism has to express what 
it cannot conceive or understand, and the capacity of adjusting most 
complex forces to meet others which it can neither measure nor weigh. 
The forces that are at work in moulding bodies are external or 
internal; amongst the latter may be placed surface tension in fluids, 
The external compression that causes a soft substance to assume a 
spherical form is more familiar to us than the mode of action of the 
cohesion forces that cause the particles to swing into position to form 
the crystalline body. Yet one may in inorganic bodies see that the 
forces that press, or the pressure that acts all around a sphere, may be 
so distributed as to form a cube, if divided into three equal pressure 
sets, each two forces acting opposite to one another on equal areas and 
at right angles to the directions of the other two pairs. The cube, 
octohedron, or dodecahedron (with rhombic base), may be easily pro- 
duced by similar compressions, and these symmetrical irregular bodies 
may be divided into two equal symmetrical parts by three planes or 
more passing through certain axes. It is evident that a quadrilateral 
symmetry may be noted in a cube lying on one side, by making 
sections with suitable planes, and a triangular symmetry in sections 
made perpendicular to a through diagonal. A suitable adjustment of 
the compressing forces leads to the production of the square prism. 
The side pairs of pressure sets will in this case be equal, whilst the end 
pair is greater or less, but each pressure pair acts at right angles to each 
of the other pressure pairs. The lateral compressing forces, if one 
opposing pair do not act at right angles to the other opposing pair, will 
give rise to a rhombic prism. The three main axes must stand at 
right angles. If the compression be so applied that an oblique prism 
is produced, one plane only can be found which will divide the crystal 
into symmetrical halves. Where a crystal is doubly oblique, the form 
may be imitated by proper pressure planes, no plane of symmetry can 
be found; symmetry here is only discoverable in individual planes. 
The hexagonal prism form seen in beryl and other minerals is con- 
nected with the rhombohedron, and the rhombohedron is a cube crushed 
out of shape. The tetrahedron and pentagonal dodecahedron are 
asymmetric crystalline forms, although regular solids. 
Angular bodies are not limited, as is well known, to inorganic 
nature. The elements of which organic bodies are composed are often 
constrained to assume forms with an angular outline. Polyhedra, 
hexagonal prisms, tessellated pavements, brick shaped and stellate cells, 
are a few of the varieties well known to the student. These forms, 
although correctly attributed to external pressure, are largely under the 
influences of forces inorganic and organic within the elements themselves. 
