Spectroscopic Observation of the Sun, No. II.

The author, after referring to his ineffectual attempts since 1866 to observe the spectrum of the prominence with an instrument of small dispersive powers, gave an account of the delays which had impeded the construction of a larger one (the funds for which were supplied by the Government-Grant Committee early in 1867), in order that the coincidence in time between his results and those obtained by the Indian obsevers might not be misinterpreted

Details are given of the observations made by the new instrument, which was received incomplete on the 16th of October. These observations include the discovery, and exact determination of the lines, of the prominence-spectrum on the 20th of October, and the fact that the prominences are merely local aggregations of a gaseous medium which entirely envelopes the sun. The term Chromosphere is suggested for this envelope, in order to distinguish it from the cool absorbing atmosphere on the one hand, and from the white light-giving photosphere on the other. The possibility of variations in the thickness of this envelope is suggested, and the phenomena presented by the star in Corona are referred to.

Two of the lines correspond with Fraunhofer's C and F; another lies 8° or 9° (of Kirchhoff's scale) from D towards E. There is another bright line, which occasionally makes its apperance near C, but slightly less refrangible than that line. It is remarked that theline near D has no corresponding line ordinarily visible in the solarspectrum. The author has been led by his observations to ascribe greatvariation of brilliancy to the lines. On the 5th of November a prominence was observed in which the action was evidently very intense; and on this occasion the light and colour of the lines at F were most vivid. This was not observed all along the line visible in the field of view of the instrument, but only at certain parts of the line which appeared to widen out.

The author points out that the line F invariably expands (that the band of light gets wider and wider) as the sun is approached, and that the C line and the D line do not; and he enlarges upon the importance of this fact, taken in connexion with the researches of Plücker, Hittorf, and Frankland of the spectrum of hydrogen---stating at the same time that he is egaged in researches on gaseous specra which, it is possible, will enable us to determine the temperature and pressure at the surfaces of the chromosphere, and to give a full explanation of the various colours of the prominences which have been observed at different times.

It is stated that, under proper instrumental and atmospheric conditions, the spectrum of the chromosphere is always visible in every part of the sun's periphery; its height,and the dimensions and shapes of several prominences, observe at different times, are given in the paper. One prominence, 3' high, was observed on the 20th of October.