Page:The story of the comets.djvu/54

30 bend in it, as if it had encountered and been turned aside by some obstacle. Near the point of deflection there were 2 dark spots in the brightest part of the tail. Finally the surviving tail split up into 6 strips. All these changes, and some others, took place in the space of 5 days.

Brooks's Comet of 1893 (iv.), discovered on Oct. 17, started with a main tail which was straight whilst there was also a secondary tail. A photograph taken on Oct. 21 revealed extraordinary changes which Barnard thus describes:—

"It presented the comet's tail as no comet's tail was ever seen before. The graceful symmetry was destroyed; the tail was shattered. It was bent, distorted, and deflected, while the larger part of it was broken up into knots and masses of nebulosity, the whole appearance giving the idea of a torch flickering and streaming irregularly in the wind. The short northern tail was swept entirely away, and the comet itself was much brighter. The very appearance at once suggested an explanation, which is probably the true one. If the comet's tail, in its flight through space, had suddenly encountered a resisting medium which had passed through the tail near the middle, we should have precisely the appearance presented by the comet. It is not necessary that the medium should be a solid body; if it possessed only the feeblest of ethereal lightness it would deflect, distort, and shatter the tail. What makes this explanation all the more probable is that the disturbance was produced from the side of the tail that was advancing through space."

Another recent comet which displayed extraordinary changes in its tail was Morehouse's Comet of 1908 (iii.), watched with great success by a numerous body of photographic-astronomers. Amongst other things some outbursts in the nature of explosions seem to have occurred in the tail. This comet is also noticeable from the fact that it travelled from Pole to Pole during the period of its visibility; and having been circumpolar during many weeks in the autumn of 1908, continuous observation for many consecutive hours was possible, which much facilitated the photographing of it.

This comet was unique from the first. The art by which it was discovered (photography) so faithfully followed its every movement, from such variety of longitudes, that a more