22 REPORT—1852. 
this action confined to “ Rupert’s drop,’’ as we have examples of the same action in 
our foundry operations in the case of masses of brittle metal, when the exterior of the 
casting, by consolidating (as it always does before the interior) the after con- 
traction of the interior of the mass, induces a sort of “‘ touch and go”’ state of tension, 
which frequently results in- such castings flying into fragments in spite of their 
apparent strength, either per se, or on the application of some force otherwise 
totally inadequate to produce so destructive a result. 
Now let us apply this action (which we find constant in the cooling of all masses 
of brittle material) to the case of the supposed parent planet of the asteroids. 
It appears to Mr. Nasmyth that we shall find in such the elements of a very feasible if 
not the true explanation of the origin of thisremarkable and numerous group of planets, 
namely, that the parent planet may haye consisted of such materials as that by the 
rapid passing of its surface from the original molten condition to that of solidifica- 
tion, while the yet fluid or semifluid interior went on contracting by the compara- 
tively gradual escape of its heat into space through the solid crust, a state of tension 
may thereby have been induced, such as that in the “ Rupert drop,” and that the 
crust may have at last given way with such violence as to cause the fragments to 
part company, and so pass whirling off into orbits slightly yarying from each other, 
according to corresponding variations in the condition of each at the instant of 
rupture. ; ; 
The remarkable fact that the orbits of these asteroids have one common node or 
point of coincidence causes us to look to some such explanation as has thus been 
hazarded, and which perhaps may be entitled, in the mean time, to fill up a gap until 
supplanted by a better explanation. 
Drawings to illustrate Recent Observations on Nebule. By the HARL 
oF Rosse. With Remarks by Rev. Dr. Ropinson. 
Dr. Robinson stated that he had examined the drawings, which contain care- 
ful delineations of several nebulz not previously examined, and certainly the 
contemplation of them was well fitted to increase the obligations of the astrono- 
mical world to Lord Rosse, as well as to fill every mind with astonishment at the 
wondrous reyelations of his matchless telescope. - Each of them was a new proof of 
a former statement of his, that this instrament would probably disclose forms of 
stellar arrangement, indicating modes of dynamic action neyer before contemplated 
in celestial mechanics. He referred to the drawings of M. 51, in which the spiral 
or yorticose arrangement of the stars and unresolved nebule was first remarked in 
its simplest form; and to others already published, where it presents itself under 
conditions of greater complexity. He also referred to the important fact that the 
class of planetary nebule might now be fairly assumed to have no existence, as all 
of them which have been examined prove to be either annular or of a spiral charac- 
ter. Thus M. 97, which was considered by Sir J. Herschel the finest specimen of 
them, and seemed even in his 18-inch reflector a uniform disc, presents in the six- 
feet a most intricate group of spiral arcs, disposed round two starry centres, looking 
like the visage of a monkey. Among the new ones are H. 2241. It is a ring of 
stars with a faiat nebula within, and a fine double star near its edge; H. 2075, of the 
same kind, but with a bright star almost exactly central, and nine others round it, 
evidently part of the same group. H. 450 is a most extraordinary object; the ring 
exactly circular, its light mottled and flickering, and within it what is evidently a 
globular cluster. Scarcely less surprising, but more magnificent from its association, 
is the planetary at the edge of M. 46, which he had seen, though in a night not so 
favourable as that must have been when the drawing was made. It is a resolvable 
double ring, rather spiral, with a central star; and from the improbability of two 
objects so rare as a splendid cluster, and one of these compound rings being casually 
connected, it seems reasonable to think they constitute one system. The double 
star, « Orionis, belongs also to this class, and he called attention to the absolute 
darkness of the aperture in the nebula round the two stars, and that the larger of 
them was at its edge instead of being central. He argued, from the remarkable dif- 

