Note 200 — Chapter X · THE CHROMOSPHERIC SPECTRUM.
Reading edition
Proc. Royal Society, vol. lxi. p. 433. Besides H and K, echoes of them survive in a pair situated so high in the ultra-violet that they can only be photographed with a specially adapted apparatus. Their wave-lengths are λ 3179 and λ 3159. They may or may not be chromospheric lines. The records so far obtained do not extend to their remote position.