Note 17 — Chapter III

“The assumption that the extent of the starry firmament is literally infinite has been made by one of the greatest of astronomers, the late Dr. Olbers, the basis of a conclusion that the celestial spaces are, in some slight degree, deficient in transparency; so that all beyond a certain distance is, and must remain for ever, unseen; the geometrical progression of the extinction of light far outrunning the effect of any conceivable increase in the power of our telescopes. Were it not so, it is argued, every part of the celestial concave ought to shine with the brightness of the solar disc, since no visual ray could be so directed as not, in some point or other of its infinite length, to encounter such a disc.”—Edinburgh Review, p. 185, for January, 1848; Etudes d’Astronomie Stellaire.