Note 661 — Chapter IV
Reading edition
Thollon's estimate (Comptes Rendus, t. xcvii., p. 902) of 300,000 kilometres, seems considerably too low. Limiting the "average prominence region" to a shell 54,000 miles deep (2′ of arc as seen from the earth), the visual line will, at mid-height (27,000 miles from the sun's surface), travel through (in round numbers) 320,000 miles of that region.