AA. FORMATION OF SHELLS OF ANIMALS, ETC., 
ceptibly blending with another, so that if these globules 
be broken up, no definite form can be detected which can 
be taken as a primary one, but everything gives indica- 
tions of their formation being due to the operation of a 
continuous force. The larger crystals, on the contrary, 
are formed instantaneously, and built up of particles of 
the same form, and doubtless of the same size, showing 
that the force which was employed in their production 
had been divided into separate impulses, each impulse be- 
ginning and ending with one of these primary forms, 
which in some degree may be taken as a measure of the 
amount and an indication of the mode of operation of 
the force employed; so that there is every appearance that 
the formation of these crystals was the result of a succes- 
sion of separate though similar impulses. Hence, the 
force producing rectilinear molecular arrangement may 
be inferred from this experiment to be impulsive, and thus 
crystals may be considered as the result of separate im- 
pulses acting upon the molecules of those substances 
which assume the crystalline form. This inference is 
particularly strengthened by the fact, that there exists in 
nature no known force, or combination of forces, which 
acting continuously and in conjunction with gravity, is 
in any way adapted to produce a sustained rectilinear mo- 
tion. It has been suggested that the electric and mag- 
netic forces (the one always intersecting the plane of the 
other’s action at right angles) are conducive to this re- 
sult; but it must be remembered, that even if the pri- 
mitive particles of matter were impelled in straight lines 
by a rectilinear current thus produced, it would not dis- 
pose them rectilinearly, unless they were solely under 
its influence—a supposition which would exclude the 
action of gravity, which has been shown by the facts of 
