The evidence at present available points strongly to the conclusion that the spirals are individual galaxies, or island universes, comparable with our own galaxy in dimension and in number of component units. [Stating his conviction on the nature of nebulae during the Shapley-Curtis debate on 26 Apr 1920 to the National Academy of Sciences.]
Heber Doust CurtisIt is certainly a wonderful, a brain-staggering conception... that our own stellar universe may be but one of hundreds of thousands of similar universes... Familiarity with these mighty concepts most certainly does not breed contempt, does not dull our awe at the mightiness of the universe in which we play so small a part. It is very doubtful if any of those who are seriously studying the heavens ever lose their feeling of reverence for this supremely wonderful universe and for Whoever or Whatever must be behind it all.
Heber Doust Curtis