The Spectrum of γ Cassiopeiæ

ON and since October 7, a very strong and very sharp absorption line, the strongest and sharpest absorption line in the whole spectrum, suddenly appeared in the spectrum of γ Cassiopeiæ. This line is nearly coincident in position with that which should be occupied by the bright violet component of Hξ. On receiving this information, Prof. A. Fowler has suggested that it is probably the neutral line of helium (λ 3888.646) intensity 10, this line being the strongest line of the principal series of the triplet system. The next line in this series is at λ 3187.743 (intensity 8), but this falls outside the region photographed at Sidmouth, so its presence cannot be ascertained.