Still another curious fact about the Pleiades, is the existence of some rather mysterious nebulous masses in the cluster. In 1859, Temple discovered an extensive nebula, of an oval form, nearly egg-shaped, with the star Merope immersed in one end of it. Subsequent observations showed that this strange phenomenon was variable. Sometimes it could not be seen; at other times it was very plain and large. In Jeaurat's chart of the Pleiades, made in 1779, a vast nebulous mass is represented near the stars Atlas and Pleione. This has since been identified by Goldschmidt as part of a huge, ill-defined nebula, which he thought he could perceive enveloping the whole group of the Pleiades. Many observers, however, could never see these nebulous masses, and were inclined to doubt their actual existence. Within the past few years astronomical photography, having made astonishing progress, has thrown new light upon this mysterious subject. The sensitized plate of the camera, when applied at the focus of a properly-constructed telescope, has proved more effective than the human retina, and has, so to speak, enabled us to see beyond the reach of vision by means of the pictures it makes of objects which escape the eye. In November, 1885, Paul and Prosper Henry turned their great photographing telescope upon the Pleiades, and with it discovered a nebula apparently attached to the star Maia. The most powerful telescopes in the world had never revealed this to the eye. Yet of its actual existence there can be no question. Their photograph also showed the Merope nebula, although much smaller, and of a different form from that represented by its discoverer and others. There evidently yet remains much to be discovered in this singular group, and the mingling of nebulous matter with its stars makes Tennyson's picturesque description of the Pleiades appear all the more life-like:
"Many a night I saw the Pleiads, rising through the mellow shade
Glitter like a swarm of fire-flies tangled in a silver braid."
The reader should not expect to be able to see the nebulæ in the Pleiades with an opera-glass. I have thought it proper to mention these nebulous objects only in order that he might be in possession of the principal and most curious facts about those interesting stars.
Orion will next command our attention. You will find the constellation in Map No. 2.
"Eastward beyond the region of the Bull
Stands great Orion; whoso kens not him in cloudless night
Gleaming aloft, shall cast his eyes in vain
To find a brighter sign in all the heaven."
To the naked eye, to the opera-glass, and to the telescope, Orion is alike a mine of wonders. This great constellation embraces almost every variety of interesting phenomena that the heavens contain. Here we have the grandest of the nebulæ, some of the largest and most beautifully-colored stars, star-streams, star-clusters, nebulous stars,