Comet b 1881

Abstract

M. CH. FIEVEZ, the Astronomer adjoint at the Royal Observatory, Brussels, has been good enough to send me a copy of his note on the analysis of the light of this comet, made with the 15-inch Merz-Cooke equatorial, provisionally installed at the Avenue Cortenberg. The polariscopic observations demonstrate that the polarisation of the nucleus was strong (très nette et bein accentuée), while that of the tail was very weak. These observations were made at several days interval, from 11h. till midnight. Sky polarisation was scarcely sensible. The spectroscopic observations proved the spectrum of the comet to consist of four bands of intensity in the following order: green, blue, violet, and yellow, with wave-lengths 5160, 4780, 4200 (about), and 5620. The original appearance of these bands was modified as the comet receded from the sun, their edges towards the red then becoming more and more defined. The nucleus presented a brilliant continuous spectrum, in which however the Fraunhofer lines were not recognised. The conclusions arrived at by M. Fievez were as follows:— That a great part of the light of the comet was inherent to it, while the other part was reflected solar light. That the strong polarisation of the nucleus indicated a marked state of condensation of the matter composing it. That the spectrum differed little from that of other comets. Lastly, that the marked modifications in the brilliancy of the continuous spectrum, and in the appearance of the spectrum bands indicated a progressive diminution in the tail as compared with that found by Prof. A. W. Wright and Mr. Cowper Ranyard, and in the absence of the Fraunhofer line, which were measured by Dr. N. de Konkoly, and also photographed by Dr. Huggins. Whence, we may ask, arises the divergence of conclusions arrived at by M. Fievez and Prof. Wright respectively, the one considering that the principal part of comet's light is from itself, the other that it is reflected sunlight, and shy were the Fraunhofer lines seen in the one case, and not in the other? The answer lies, I think, not with the instruments employed, but rather in the interesting probability of change in the comet's structure or condition during the time of its examination. A comparison of the many observations recorded during its stay with us may possibly lead to important discoveries in this direction. I am much interested to see that Prof. C. A. Young informs us that the green band was seen by observers at Princeton split up into fine sharp lines coinciding with those seen in the flame spectrum, a result to be expected, but hitherto not attained.