From: george murphy (
Date: Wed Jan 30 2002 - 12:22:46 EST

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            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
    in 1936.)
            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
    HII regions.
            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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