Page:The story of the comets.djvu/241

XII. comet) was amply affirmed, for on spectra obtained by Mr. and Mrs. Evershed, at Kodaikanal, India, and by Deslandres, at Meudon, it was found that the radiations of the nucleus were not identical with those of the tail. Evershed photographed the spectrum of Procyon alongside that of the comet, and was thus able to determine the wave-lengths of the cometary spectrum by direct comparison with the hydrogen lines in that of the star.

The last comet to be considered here is the one discovered by Morehouse on September 1, 1908.

No other comet has ever been so well, and so persistently, observed, and certainly no other cometary spectrum ever received so much detailed attention. Whilst the object itself was remarkable for its vagaries, its lightning changes of form, and its periodic outbursts, the spectrum observations were, at first sight, almost as remarkable for their positive disagreements. This may have been due, however, to some extent, to the fact that so many observers were at work at different times.

Count De La Baume Pluvinel and Baldet photographed the spectrum, with the prismatic camera, on October 4, 5, and 7. The plates obtained showed seven monochromatic images of the comet and indicated that the hydrocarbon radiations—strong in the spectrum of Daniel's Comet, obtained with the same instrument—were absent: the cyanogen spectrum, usually represented by the band at 388 alone, was completely represented in the part of the spectrum photographed, and there was no trace of continuous spectrum.

Evidence of change was afforded by the radiation at 376, for whilst a tail accompanied the feeble image photographed on October 5, there was no trace of it on the more intense, nuclear image of October 7.

Deslandres and Bernard agreed on the absence of the hydrocarbon radiations. But they found the two first heads