SCIENTIFIC NEWS. 
77 
The 3d and 4th sections g’ve a rapid view of the geometrical 
definitions employed in crystallography — the admeasurement 
of the angles of crystals, with a description and use of the 
goneometers of Wollaston and Carangeau employed for that 
purpose. 
The 2d part commences with a general view of the con- 
stitution of bodies, and a sketch of the theory of crystallography 
of Haiiy — it is there shown, that all crystals, however com- 
plicated their forms may be, contain within them a geome- 
trical nucleus, called by Haiiy the primitive form, which 
has, under certain restriction, an invariable shape in each 
chemical species of crystalline solid, and which may be extract- 
ed out of all of them, by a skilful mechanical dissection. 
The 2d section of this part, shows the mechanical dissections 
of crystals, to develope the primitive forms, their nature, their 
number, and situations in different bodies, and general inferences 
relating to the mechanical analysis of crystalline bodies in 
illustration of the theory. The dissections are illustrated by 
graphic projections, and rendered farther striking to the senses 
by dissected models, of which references are made. 
But the primitive forms of crystals which are considered as 
bodies of a constant geometrical form, inscribed symmetrically 
in all the crystals of one and the same chemical composition, 
are not the ultimate result to which the mechanical dissections 
of crystals may be carried. 
The 3d section shews, that the primitive forms of crystals are 
divisible in a direction parallel to their faces, and sometimes also 
in other directions, and this in the latter case must produce 
solids, which differ in shape from the primitive crystal to which 
they belong, and these solids, thus obtained by different modes of 
dissections, are called, by Haiiy, the integrant panicles of 
crystals. To illustrate this statement, numerous examples are 
given. The sketches and dissected models advanced on this 
occasion are the following : the rhomboid of the tourmalin — the 
hexahedral prism of phosphate of lime-- the cube of fluate of 
lime, &c. &c. 
The 4th section, in a similar manner, elucidates the laws of 
decrements of the structure of crystals, or the laws of crystalline 
architecture, according to which are produced those ariange- 
ments 
