20 
THE NEBULAE HYPOTHESIS: ITS PRESENT 
CONDITION. 
By JOHN J. PLUMMER, M.A. 
I N the whole range of science there is no theory which has 
attracted so much attention, has passed through so many 
vicissitudes, and has been so earnestly and fondly supported in 
the face of opposing evidence, as the nebular hypothesis of 
Laplace. This has arisen, doubtless, to some extent from the 
respect due to the very eminent astronomers by whom it was 
first suggested and promulgated, but perhaps still more to the 
nature of the hypothesis itself, and to the fact that many 
otherwise unexplained phenomena find in it a satisfactory solu- 
tion. The whole course of scientific progress has led us to look 
for the most simple laws in order to explain the most appa- 
rently complicated results ; and such a law the nebular hypo- 
thesis would become, were it possible to give to it such a high 
degree of probability as at present serves for the demonstration 
of the Newtonian law of gravitation, or of the undulatory theory 
of light. That it may one day attain to this degree of cer- 
tainty, and be recognised as an established truth, is the hope of 
many who are fascinated alike by its simplicity and its compre- 
hensiveness — a hope that has often served to sustain it when 
the bulk of evidence has not appeared to be in its favour, and 
one in which the writer to some extent indulges, although well 
aware that it may require to undergo considerable modification 
before it reaches that exalted position. 
Previously to the revelations of the spectroscope, the nebular 
hypothesis stood at a very low ebb. The gradually increased 
powers of telescopes, culminating in the gigantic reflector of 
Lord Rosse, had one by one reduced the number of the so-called 
nebulae, by resolving them into clusters of distant stars, very 
closely packed together, until, although a large number still 
continued nebulous in appearance under all circumstances, it 
seemed very probable indeed that indefinitely increased tele- 
scopic power was all that was needed to resolve the remainder. 
Still it retained a few believers, loth to relinquish the insight 
