History: When were other galaxies `discovered`?

Hi,

While reading up for an essay I came across a paper by Harlow Shapley from 1917. [1]

In it he makes references to `spiral nebulae` and in particular that `it appears unlikley that the spiral nebulae can be considered separate galaxies of stars` and that they are instead `members of the galactic organisation, appearing to avoid the regions of enormous masses and forces`.

I had thought that with the advent of large telescopes the structure of galaxies such as the andromeda galaxy would have been apparent, and cephid variables would have been able to give an indication of distance. That technique was used for estimating distances to globular clusters for example.

So when did we work out that the `spiral nebulae` really were distant objects and how? Were cephids not detectable in other relativly nearby galaxies until much later in the century?

Cheers,
~Al

[1] adsbit.harvard.edu/cgi-bin/nph-iarticle_...=1918PASP...30...42S

Edwin Hubble resolved the great Shapley-Curtis debate on the extent of the Universe by, amongst other things, identifying Cepheid variable stars in the Andromeda Galaxy (M31). These stars allowed Hubble to show that M31 was in fact much more distant than Shapley's proposed extent of the Milky Way, and was therefore a separate galaxy much like our own.

See antwrp.gsfc.nasa.gov/htmltest/gifcity/cs_why.html for more on this.