1868. } Sir John Herschel and Modern Astronomy. 189 
Series 1, including 881 new double stars. 
ee i 295 more new double stars. 
vn CWS n 384 more new double stars. 
4, re 1,236 double stars, the greater part not 
previously described. 
These observations were continued with the most untiring 
industry, and in 1832, Mr. Herschel published, as a fifth series, a 
catalogue of 2,007 double stars, of which 1,304 were new, and a 
sixth series was produced in the following year. In the ‘ Philo- 
sophical Transactions for 1833’ there is a valuable communication, 
“Observations of Nebule and Clusters of Stars,” with a 20-foot 
reflector. In this memoir we have a most careful examination of 
all the conditions observed in star-clusters and nebulous masses. 
Some two thousand of these mysterious classes of bodies were 
examined, and their physical construction, as far as possible, is 
described. The result of all this labour may be examined with 
much advantage in the ‘Outlines of Astronomy.’ In the para- 
graphs of that work which are devoted to this subject, the specula- 
tions of Sir William Herschel are cautiously reviewed. The 
“nebular hypothesis,” as it has been termed, supposes the existence 
of an elementary form of luminous siderial matter, and its gradual 
subsidence and condensation by the effect of its own gravity, into 
more or less regular spherical or spheroidal forms. “ Assuming 
that in the progress of this subsidence local centres of condensation, 
subordinate to the general tendency would not be wanting, he (Sir 
W. Herschel) conceived that in this way solid nuclei might arise, 
whose local gravitation still further condensing, and so absorbing 
the nebulous matter, each in its immediate neighbourhood, might 
ultimately become stars, and the whole nebulz finally take on the 
state of a cluster of stars.” Sir John Herschel’s leaning towards 
this view will be evident from the following remarks :—“ Among 
the multitude of nebulz revealed by Sir W. Herschel’s telescopes, 
every stage of this process might be considered as displayed to our 
eyes, and in every modification of form to which the general 
principle might be conceived to apply. The more or less advanced 
state of a nebula, towards its segregation into discrete stars, and of 
those stars themselves towards a denser state of segregation round a 
central nucleus, would thus be, in some sort, an indication of age. 
Neither is there any variety of aspect which nebule offer which 
stands at all in contradiction to this view.”* 
Another contribution to astronomical science was his ‘ Observ- 
ations on the Satellites of Uranus,’ published by the Astronomical 
Society; and this was followed by two series of micrometrical 
measurements of double stars, made at Slough with a seven-foot 
Equatorial. 
* “Outlines of Astronomy,’ pp. 598, 599. 
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