The discussion about Whewell, telescopes, galaxies &c has died
down in my absence. I think my comments over a week ago took the
discussion off on something of a tangent. I think Glenn made a good
point about the tendentious character of Whewell's arguments & have no
particular interest in defending him (Whewell). Here I just want to
add, for the sake of completeness, a few comments about the debate
concerning the "nebulae."
1) It's important to remember that what were referred to as
"nebulae" in the middle of the 19th century included both objects now
known to be external galaxies and those that are within our galaxy.
When writers of Whewell's time refer to "the nebulae" being resolvable
into individual stars, it's often not clear if they're referring
specifically to those now known to be galaxies. (This ambiguity
persisted long after the extra-galactic character of some of these
objects was settled: Hubble's _The Realm of the Nebulae_ was published
2) It was certainly known well before 1920 that individual
stars could be identified in some of the debatable "nebulae". It's not
so clear that such identification was beyond challenge 70 years
earlier. While Lord Rosse's telescope was an impressive instrument, it
should be remembered that at that time neither photography nor spectral
analysis were common tools of astronomers. Of course a skilled observer
may "see" more than he or she can put down on paper, but the sketches of
spirals by Lord Rosse (e.g., Berendzen _et al_, p.15) don't give much
indication of their stellar character.
The use of spectroscopy failed for some time to settle the
question & if anything seemed to weigh against the stellar character of
these nebulae because of the failure to identify absorption lines.
E.g., in 1898 Arthur Berry wrote (in _A Short History of Astronomy_),
"The 'island universe' theory of nebulae, partially abandoned by
Herschel after 1791 ... but brought into credit again by Lord Rosse's
discoveries ... scarcely survived the spectroscopic proof of the gaseous
character of certain nebulae."
3) Finally, some identifications of individual stars in
external galaxies may have been wrong, & this was the case even after
1920. One of the errors that led to Hubble's originally very low vale
for the age of the universe (less than 1.8 x 10^9 yr) was the fact that
what he thought were the brightest stars in some galaxies were in fact
All this means, I think, is that there was some ambiguity about
stellar character of the "nebulae" in the latter part of the 19th
century. The really crucial question though, as Glenn correctly noted,
was not their stellar character but their distances.
George L. Murphy
"The Science-Theology Interface"
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