Slipher and the Nature of the Nebulae

TL;DR

This paper examines why Vesto Slipher's early nebular redshift discoveries, which suggested extragalactic origins, had limited impact initially due to contemporaneous errors and scientific context, delaying recognition of their significance.

Contribution

The paper analyzes historical reasons behind the delayed recognition of Slipher's nebular redshift discoveries and contrasts them with other paradigm-shifting but initially overlooked findings.

Findings

Slipher observed nebular redshifts up to 1000 km/s by 1914.

Van Maanen's erroneous work obscured Slipher's findings.

Slipher's discoveries were partly recognized but their full significance was delayed.

Abstract

Why do some discoveries, which appear in hindsight to be obviously major discoveries, have so little impact when they were made. These are discoveries that were ahead of their time, but for some reason the scientific community was not ready to absorb them. I got interested in Slipher after learning that by 1914 he had observed nebular redshifts up to 1000 km/s. Why did this not convince people at the time that the nebulae were extragalactic ? Was this another example, like Zwicky's (1933) discovery of dark matter in the Coma cluster, of a discovery which was too far ahead of its time ? I conclude that Slipher's situation was different from Zwicky's. The significance of Slipher's nebular redshifts was partly recognised at the time, but I believe that its full significance was masked by van Maanen's work which turned out to be erroneous and reduced the impact of Slipher's discoveries.