Page:The story of the comets.djvu/67

III. day. Condensations, waves, straight rays, twisted funnels, and numerous unrecognised forms made up its wonderfully active tail.

Not only was it exceptional in its actions, but also in its constituent material. Its spectrum was quite different from previous comets. In place of the familiar hydrogen gas was found the poisonous cyanogen element. Other ingredients not recognised seem to have been present. Altogether it gave to astronomers a wealth of data which it will require years to digest and interpret properly.

The literature of comets' tails may be likened to the literature of Free Trade and Tariff Reform in the world of Politics: it is superabundant and more than superabundant. In the pages which have gone before I have somewhat exhaustively described these tails from the standpoint of the mere stargazer, armed, or not, as the case may be, with a telescope. It remains now to consider, and I shall do so very briefly, some of the more definite conclusions which have been arrived at as to the theory of tails; by which is meant the dynamical circumstances under which they are usually evolved. Speculation as to this has proceeded of late years on a gigantic scale, and vast quantities of ink and paper have been (as I think fruitlessly) expended on the subject, the details of which would not have much interest for the general reader.

It is to a Russian astronomer, Bredichin, that we owe what seems the most thoughtful and best classification of comets' tails; and his conclusions are the more valuable that they do not run into extravagances of speculation. Briefly stated, he divides the tails of comets into 3 classes or types:— Rh