BY MOLECULAR COALESCENCE. 47 
demonstrate exactly in what manner the electrical force 
must act upon the molecules of these calculi, as well as 
upon those of other crystallizable substances in the act of 
crystallization, so as to give them that crystalline arrange- 
ment which they have been shown suddenly to acquire, 
it will be necessary to divide, mentally, this process into 
different parts, and to investigate these separately, and 
afterwards to consider them as they would act together. 
First, then, let the molecules about to take on the crys- 
talline form be: supposed to be in isolated groups, one 
group being incapable of influencing the other; and 
suppose that im an instant all these molecules become 
endowed with the power of repelling one another, and it 
will be obvious that the molecules of each group will 
suddenly become divergent and tend to arrange themselves 
in a spherical form, of which the central molecule of the 
group, retaining still its position, will be the centre, whilst 
all those around it will be thrown into diverging lines or 
radii goig from that centre. Next, suppose two such 
groups of equal size, placed side by side, to be acted upon 
in the same manner as the above, and it will be at once 
apparent that, as their adjacent molecules are impelled in 
directions which intersect one another, their motion beyond 
the point of intersection would be retarded and the force 
communicated to them diminished, the 
y degree of diminution being as the sine 
an of the angle a, c, B (see the accom- 
) panying diagram). Hence, at the 
point a the line a, 8 will denote the 
amount of the attraction of gravita- 
tion necessary to balance the force 
of impulsion acting on the molecules 
at a, and so to bring them into the condition of rest. 
