Page:Gods Glory in the Heavens.djvu/171

Rh as the stream of fiery particles issues from a rocket. They rush out towards the sun with great velocity, but soon they reach a certain point, when they are driven back to form the tail. The appearance is not unlike that of a lighted torch held against the wind. The tendency of the flame to rise is counteracted by the action of the wind, which drives it back. The most perfect illustration we have seen of the internal form and movement of the comet, was the playing of the fountain in the garden of the Tuileries, close to the Place de la Concorde. The water rose to a considerable height, and fell back in an umbrella form. There was a slight wind, and the jet was slightly curved along its length, as in the case of the comet. The windward side was also best defined, the loose spray being all thrown to the leeward side. The descending canopy being hollow, the outline of both sides was more condensed than the central part, the eye having to look through a greater mass of water. The luminous particles shoot forth from the nucleus, just as the water spouts forth from the jet, and are thrown back to form a hollow envelope. The curvature of the comet, and the sharper definition of the convex side, are usually explained on the supposition that the comet is moving through a resisting medium, so that an effect similar to the influence of the wind on a jet-d' eau is produced.

In the case of Donati's comet, the telescope detected the formation of numerous envelopes, so that