Abstract
THE PRESENCE OF OXYGEN IN THE SUN.—At the meeting of the Paris Academy of Sciences on April 9, Dr. Janssen described a convenient method of raising gases to a high temperature, used by him in connection with investigations on the spectrum of oxygen. The question of the presence of oxygen in the gaseous envelopes of the sun comes under two distinct cases. In the first place, oxygen may exist in the exterior parts of the corona, that is to say, in a medium where the temperature approaches that of the terrestrial atmosphere. In this case the spectrum of the gas would be similar to that which is produced by our atmosphere, and, in order to prove its absence in such parts of the coronal envelope, it is sufficient to show that the lines and bands due to oxygen in the solar spectrum are entirely produced, both as regards number and intensity, by the earth's atmosphere. Dr. Janssen's observations from the summit of Mont Blanc, and his experiments at Meudon, have been made with a view of settling this point. But the case of observations on oxygen at ordinary temperatures only represents a part of the question. Any oxygen existing in the lower portions of the corona, in the chromosphere, and in the photosphere, must be at a high temperature, and in order to decide, by means of spectrum analysis, as to whether it is present or not in these solar layers, it is necessary to know the modifications which the spectrum of oxygen undergoes when the temperature of the gas is elevated. This research, however, is attended with special difficulties. The absorption lines and bands of oxygen are only produced by great thicknesses of the gas. The B group, for example, only appears in the spectrum when a luminous beam has traversed a thickness of 60 metres of the gas under the pressure of two atmospheres. The dark band situated near D requires for its production a thickness of 60 metres at a pressure of six atmospheres. It is extremely difficult to raise such long columns of gas to high temperatures, and the better plan is to reduce the length and increase the pressure. By means of an electrical method, Dr. Janssen has been able to heat a column of oxygen to incandescence without sensibly heating the tube containing the gas. He has used a steel tube 2˙2 metres long and about 6 centimetres in external diameter, with an internal diameter of 3 centimetres. This tube is able to resist pressures of over 1000 atmospheres. The temperature of the gas is raised by means of a platinum spiral traversing the length of the tube, and insulated from it by means of a layer of asbestos. Dr. Janssen will shortly give an account of the results obtained when oxygen was introduced into the tube, heated, and spectroscopically observed.
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Our Astronomical Column. Nature 49, 585–586 (1894). https://doi.org/10.1038/049585a0
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DOI: https://doi.org/10.1038/049585a0