1872.| The Construction of the Heavens. 323 
heavens, have prepared the way for a final investigation of 
the universal arrangement of all these celestial bodies in 
space.” He was now in his seventy-sixth year, however, 
and though still in the full possession of his wonderful 
powers, the time that remained to him for investigating the 
universal arrangement of the heavens was short indeed, 
when the wideness of the subject is considered. But 
he was not even yet fully prepared to enter on the work. 
For he proceeds to mention as a reason for not doing so, 
that he is “still engaged in a series of observations for 
ascertaining a scale whereby the extent of the universe, 
as far as it is possible for us to penetrate into space, may be 
fathomed.” 
In the papers of 1817 and 1818, the last of the series, and 
written, be it remembered, when Herschel was in his seventy- 
eighth and seventy-ninth years, he describes the principle 
here referred to, and its application to estimate the pro- 
fundities of various parts of the stellar heavens. The 
principle was essentially this—that the telescopic powers 
necessary to reveal and to resolve star groups, or particular 
star orders within groups, afford an indication of the dis- 
tance at which those groups or orders lie. I conceive that 
no question can exist that the principle is unsound, and that 
Herschel would himself have abandoned it, had he tested it 
earlier in his observing career, and when not his mental 
power, but his mental elasticity, was greater than at the 
advanced age which he had now reached. I have not here 
space to enter into all the objections which present them- 
selves against it. Presently, in considering Sir John 
Herschel’s theoretical views, I shall have to adduce a con- 
clusive instance of the unsoundness of the principle. Let 
it here suffice to remark, that repeatedly in applying it, Sir 
W. Herschel found regions of the heavens very limited 
in extent, where the brighter stars (clustered like the 
fainter) were easily resolved with low powers, but where his 
largest telescopes could not resolve the faintest. These 
regions, if the principle were true, must be long spike- 
shaped star groups, whose length is directed exactly towards 
the astronomer on earth,—an utterly incredible arrange- 
ment, even if we could believe in the dynamical possibility 
of such grouping. 
Herschel did not live to carry out that final investigation 
of the universal arrangement of all the celestial bodies 
in space which he had looked forward to in 1814. In 1820 
he read, as first President of the Astronomical Society, a 
paper on the double stars, and soon after his health broke 
