those of a Cygni was pointed out. Later, Mr. McClean* confirmed this, and further stated that the bright lines of 77 Argus corresponded with the dark lines of the Nova ; while later still, Sir David GiUf has shown the similarity between the spectra of rj Argus and Nova Aurigse. Hence we are led to the conclusion that the temperatures reached in the outbursts of both these Novae were not greatly different from those of the stars named, and that in t\ Argus there are constant con- ditions which are similar to those temporary conditions which produce the appearance of Novas.
In the table the lines of Nova Persei are compared with those recorded by Campbell J and Vogel in Nova Aurigse.
The probably corresponding lines of a Cygni, chromospheric lines, and enhanced lines, are also given in separate columns.
The reduction to wave-lengths and discussion of the lines in relation to those of other celestial and terrestrial spectra, has been undertaken by Mr. F. E. Baxandall, to whom my best thanks are due.
In my paper on " The Boiling-point of Liquid Hydrogen determined by Hydrogen and Helium Gas Thermometers "|| it was pointed out that a constant-volume gas-thermometer filled with oxygen gas, having a pressure at C. of about 800 mm., gave a very accurate value of the boiling-point of liquid oxygen. As it seemed advisable to confirm this result indirectly, an attempt was made to determine the vapour density of oxygen at its boiling-point by direct weighing, the intention being, if the experimental results proved at all encouraging, to repeat the work on a larger scale and with greater precautions. As at present there is no likelihood of my being able to undertake the more accurate determinations, the results of the preliminary enquiry are presented to the Society. They give in any case, with considerable accuracy, the Specific Volumes which have never been directly determined.
In order to obviate any question of the buoyancy of the air, two flasks A and B of as nearly as possible the same air displacement were counterpoised on an (Ertling balance. The B flask remained per-
- ' M.N., E.A.S.,' vol. 61, p. 387.
f ' Eoy. Soc. Proc.,' vol. 68, p. 457. % ' Ast. and Ast. Phys.,' vol. 11, p. 808. ' Asfc. and Ast. Phys.,' vol. 12, p. 912. || Eoy. Soc. Proc.,' vol. 68, 1901.
