Page:Proceedings of the Royal Society of London Vol 69.djvu/142

134 The magnitude has been estimated on sixteen evenings. These seem to afford sufficient evidence that since the beginning of May the star has decreased in magnitude from about 5 -7 to 6'7 ; further, the short variations previously recorded apparently no longer exist, as the esti- mated magnitudes on eleven nights since the end of August only vary between 6'5 and 6 '8.

Photographs of the region about the Nova were taken with the 6-inch Dallmeyer doublet on the evenings of August 25 and September 11, 12, and 18. From these it has been ascertained that its magnitude relatively to those of the surrounding stars is greater photographically than visually.

The spectrum has been observed with a McClean direct-vision spectroscope on the evenings of August 8, 13, 17, 20, 22, 24, and September 11, 12, 18. The line in the position of the chief nebular line at A 5007 has always been noted as being the strongest, lift and the line at A 4959 being also present, but comparatively much weaker. Fairly bright lines near A 472 and the region of Hy have also been recorded. Traces of a few lines less refrangible than A 5007 have been glimpsed, but no determinations of their wave-lengths have been made. No lines have been observed in the yellow or red regions of the spectrum.

Photographs have been taken on the evenings of August 9, 15, 17, 21, 22, 23, 24, 26, September 3, 5, 9, 10, 11, 12, 18, 21, 23, 25, 2G, with the 9-inch prismatic reflector, the Nova being now far too faint for the utilisation of the 6-inch objective prism, and, until quite recently, in such a position as to make the 30-inch reflector unavail- able. These photographs show little or no variation amongst themselves either in the number, position, or relative intensities of the lines. The scale of the photographs is such that the distance between Hft and He is about 0'9 cm. The wave-lengths of the lines have been determined from the best photograph (August 26) by means of an interpolation curve. The presence in the Nova spectrum of some of the hydrogen lines and the helium line A 4471 was established by direct comparison with the spectra of other stars photographed with the same instrument. These lines were used, together with the 5007 line (the identity of which with the strongest nebula line was assumed), as fiducial lines for the construction of the interpolation curve. The remaining lines were then measured and their wave-lengths read off from the curve. The intensities of the lines as they appear on the plate were also noted.