200 Notices respecting New Books. 
form produced by the cause above descr’bed, the surface of a 
body is never equally acted upon by a solvent. Stria or ridges 
may he detected in various places, and, indeed, generally cover 
the whole of its snperficies, which prove, not only that the me- 
chanical attraction of the solid has resisted chemical action, but 
that it has resisted it more in some directions than in others. 
The flowing expe.iments, which only require time and moderate 
attention, while they give determinate results, are explanatory, at 
once, of the cause and progress of the phenomena. 
‘¢ If we immerse an amorphous mass of alum in water, and 
set it by in a place where it may remain undisturbed for a period 
of three or four weeks, at the expiration of that time we shall 
find that it has assumed the pyramidal form before described. 
Upon a further examination, we shall observe that the lower end 
of the mass presents the form of octohedrons and sections of oc- 
tohedrons, as it were, carved or stamped upon its surface. These 
figures will be high in relief, and of various dimensions.—They 
will be most distinct at the lower extremity, becoming less so as 
they ascend, till at length they are totally obliterated. 
** A continuation of the process, however, would evidently re- 
solve the whole into similar figures, their cessation arising solely 
from that superior power of solution which subsists in the upper 
stratum of the liquid. 
“¢ These crystalline forms are produced when the water is pare 
tially saturated with the salt, and acting with diminished energy 
is nearly counterbalanced by its mechanical structure; and we 
are thus put in possession of the important fact, that this latter 
power does not merely act, as has been hitherto supposed, in the 
grosser forms of aggregation, but in the more complicated and 
delicate arrangements of crystalline polarity. 
‘¢ This regular structure is developed both when we employ an 
amorphous mass and a regular crystal, proving that the ultimate 
arrangement of particles is the same in both; and that the like 
disposition exists, both when the slowness of approximation has 
bounded the solid with symmetric planes, and when the sudden- 
ness of the condensation has forced the aggregated molecules into 
a more contracted space. 
‘* This new process of dissection admits of more extensive ap- 
plication than might at first be imagined, and we are thus fur- 
nished with a method of analysing crystalline arrangements, which 
promises to lead to important results. The geometrical figures 
produced by these means, are not less determinate when the 
process has been carefully conducted, than those which result 
from the common methods of crystallization; and they are the 
more instructive, inasmuch as we are presented in the same group 
with an extensive series of modifications, and decrements of the 
primitive 
