BY MOLECULAR COALESCENCE. 13 
is the only way of accounting for them—that is, that they 
result from the union and intimate blending together of 
pre-existing minuter particles. The same train of reason- 
ing applies equally to the larger and more complex forms 
of these calculi, as represented in Figs. 3 and 4, with this 
additional fact, that the secondary forms, which by their 
union form the largest calculi, possess characters suffi- 
ciently marked to render them individually recognisable, 
both when grouped together into spherical masses to 
form compound calculi, and when passing through their 
various changes of form, even almost up to their complete 
coalescence into one perfectly spherical body. For the 
satisfactory examination of these changes of form polarized 
light is indispensably necessary. Now, as insuch a group 
as that represented at fig. 3, c, there is no mechanical 
reason deducible alone from its general figure which can 
account for the fact of its contour bemg made up of arcs 
of very different lengths, though of circles of nearly the 
same radius, and for the arcs of the two extreme pieces 
being each of them so much longer than that of the mid- 
dle piece, the explanation must be sought for in some 
cause which had acted upon the individual fragments ; 
but as there is no conceivable combination of mechanical 
forces which could have produced one part of any one of 
these fragments of spheres without at the same time pro- 
ducing its counterpart, these pieces must have had, when 
separate, a form different to that which they have when 
combined, and that form, from the figure of the different 
fragments, may be inferred to have been spherical. Hence 
it remains now to demonstrate in what manner the spheri- 
eal figure is first given to the component globules, and, 
after that, to show how these become incorporated m 
those of the larger size, so as to result in the production 
