D. Trowbridge on the Nebular Hypothesis. 347 
of the materials composing it, and perhaps other things—that 
the fluid would cool unequally in different parts, and in such 
places it would condense unequally, and thus, if they did not 
already exist, different centres of attraction would be produced, 
Around these different centres, matter would accumulate and 
condense, and these nuclei, so formed, would revolve around 
their common centre of gravity. As soon asa rotatory motion 
ad commenced, centrifugal forces would begin to act; and as 
the process of cooling continued, the attraction of gravitation 
would have a greater control, (for the tendency of heat is to ex- 
oa all bodies, and thus to operate against the attraction of co- 
esion, and also of gravitation in the case which we are consid- 
ering,) and thus the mass would be condensed, and the rotatory 
motion thereby increased. But an increase of rotatory velocity 
would also increase the action of the centrifugal force, and this 
process would continue until in some parts the centrifugal force 
might equal the force of gravity, and a separation would take 
place; and in this way each nucleus might ultimately be sepa- 
rated from all the others, when each would pursue its own course 
around the common centre of gravity of the whole. 
7. Each nucleus would itself be in a condition very similar 
to that which at first existed in the original great flui 
The same laws and forces acting on each nucleal mass, would 
Senerate a motion of rotation, if the previous separation had 
hot already given it an initial rotatory velocity,’ and this mo- 
tion would generate a centrifugal force, as befvre, and each of 
Nese masses would separate into parts. This process of separa- 
ton would continue until such a result could no longer ensue, 
During all this time, it must be recollected that the original nu- 
eleal parts would continue their revolutions around their common 
eentre of gravity, while the parts into which each original nu- 
Cleus was divided would continue their revolutions around their 
common centre of gravity. In this way each division, or sys- 
tem, would continue its own independent revolution, and at the 
Same time it would be earried around the common centre of 
gravity of the greater system of which it formed a part; just as 
satellites revolve around their primaries, while the primaries 
are at the same time carried around the sun, and the sun around 
Some more distant centre. It is in this way that we would ac- 
Count for the existence of clusters of stars. 
8. Notwithstanding the probability that the detached parts 
Would have a motion of rotation impressed upon them, yet we can- 
Not so easily infer that this motion would be in the same direction 
