[13] My references to ‘perfect gas of the density of platinum’ and ‘material 2,000 times denser than platinum’ have often been run together by reporters into ‘perfect gas 2,000 times denser than platinum’. It is scarcely possible to calculate what is the condition of the material in the Companion of Sirius, but I do not expect it to be a perfect gas.
[14] Photographed by Dr. W. H. Wright at the Lick Observatory, California.
[15] Nos. 43, 61, 75 are recent discoveries and may require confirmation. There now remain only two gaps (85 and 87) apart from possible elements beyond uranium.
[16] It does not give both temperature and pressure, but it gives one if the other is known. This is valuable information which may be pieced together with other knowledge of the conditions at the surface of the stars.
[17] Hydrogen (being element No. 1) has only one planet electron.
[18] [Fig. 9] is a photograph of the ‘flash spectrum’ of the sun’s chromosphere taken by Mr. Davidson in Sumatra at the eclipse of 14 January 1926.
[19] The helium line in the Ring Nebula on which we have already commented is not a member of the Pickering Series, but it has had the same history. It was first supposed to be due to hydrogen, later (in 1912) reproduced by Fowler terrestrially in a mixture of helium and hydrogen, and finally discovered by Bohr to belong to helium.
[20] This, of course, is found from the other lines of the spectrum which genuinely belong to the star and shift to and fro as it describes its orbit.
[21] As the word temperature is sometimes used with new-fangled meanings, I may add that 15,000° is the temperature corresponding to the individual speeds of the atoms and electrons—the old-fashioned gas-temperature.
[22] Photograph taken by E. T. Cottingham and the author in Principe at the total eclipse of 29 May 1919.