J. D. Dana on Cohesive Attraction. 101 
_In the case before us, each of the six rays has a series of 
short crystals along the margin, producing what Botanists call a 
pinnate form. 
_ As the crystal enlarged, these branchlets were formed at inter- 
vals by twos. ‘There was an interval in which the sides of the 
ray produced no branch; ahd then another where a branchlet be- 
gan on either side; and so on successively, as the erystal indicates. 
_ The moment of production for the six rays severally was the 
same for each, for there are corresponding branchlets on each, at 
_ the same distance from the centre. 
_ The interval between the successive productions was equal ; 
for the branchlets are the same distance apart. 
_ The rate of increase corresponded in each parallel series, for 
the branchlets at equal distances from the centre are equal. 
Hence, the action of the attracting force was in some degree 
regularly and uniformly intermittent. 
_ Again we observe that the branchlets are equal throughout 
instead of being longer towards the base of each ray, where they 
were first formed. As the ray increased at the extremity, it pro- 
duced its lateral branchlets after attaining a length beyond a 
former branchlet equal to the interval separating two branchlets. 
And the branchlet produced, increased for a certain period of time; 
till a specific length was attained, and then ceased to enlarge. 
Thus growth took place at the extremity according to a regular 
law of intermission. The extremity elongating, produced its pair 
of lateral branchlets, after a certain interval, while parts of the star 
nearer the centre did not increase; or they increased so equally 
throughout, that a perfect uniformity in size was retained. Hence 
the attracting force was most active at the extremity, and its 
condition of activity determined the length of interval between 
the successive side-developments. In other words ae 
_ The force of attraction was active only for a limited distance 
from the apex of each ray; its action was apical alone, until the 
ertremity had increased to a definite length, and then lateral ac- 
tion ensued, producing on each side a branchlet ; this length of 
apex to which the force is in a state of activity, may perhaps de- 
termine the length of the side branchlets. gry 
_ From the various figures given by Scoresby, many variations 
in the condition of this force are readily deduced; we do not 
enter fully into this subject, as we should prefer first to ver ify his 
igures. The general fact however is too plain to be mistaken. 
_ With a different condition in the force at the extremity, and in 
its relation to that in the sides of the rays, a hexagonal plate 
may result instead of a star; the condition should be such that 
there would be laterally a continuous imstead of intermittent 
increase of the rays. : : 
