To give a better idea of the structure of the Milky Way, two photographs are here reproduced as taken by Wolf, the German astronomer in Heidelberg, who has done particularly meritorious work in this department. One (Fig. 6) shows a section of the Galaxy in Cygnus (the Swan) with the star Deneb in the centre and to the left the “Northamerican-nebula” so named from its shape. Above Deneb is the dark “hole” in Cygnus and below another chasm not quite so black. Left of the “hole” is the winding canal enclosing the so-called Cocoon nebula. (See _Worlds in the Making_, page 172.) The following picture (Fig. 7) contains, in the upper left, the bright star Altair in Aquila (the Eagle) located close to the powerful arm of the Galaxy in this constellation. Farther to the right is the fainter arm in Ophiuchus (the Serpent-holder). The lower half contains the most brilliant part of the Milky Way in the constellations Scutum (the Shield) and Sagittarius (the Archer). Bright stars are infrequent but the fainter ones are innumerable: “They are crowded into dense clusters and between them the most delicate star dust is scattered.”--“We behold how the star-ribbon dissolves into detached tufts which intertwine into the strangest patterns. These clouds of stars reach their greatest splendour in the lower part of the map.” [Illustration: Fig. 6. The Milky Way between constellations Cassiopeia and Swan from photo by M. Wolf of Heidelberg. A little to the left of the middle the beautiful nebula America appears. ] [Illustration: Fig. 7. The Milky Way in constellations Eagle (upper half) and Archer (lower half). In the upper left the bright star Altair appears. Photo from M. Wolf of Heidelberg. ] We also reproduce (Fig. 8) from M. Wolf a photograph in larger scale from the region of Gamma (lower part of Fig. 7) in the Eagle with its “trident-hole,” so called from its peculiar shape, and in whose vicinity mists and star-clouds abound. This picture is a more complicated counterpart of the flatter photograph by Wolf of the “Cocoon nebula.” It appears as if three or four stellar bodies here had stepped in from without, swept away the stars in their way, and left clean “streets” behind. Probably other “empty” spots in the neighbourhood have been formed in a similar manner. Another theory is that such dark places are caused by opaque mist-formations which shield the light of the stars behind from our sight. [Illustration: Fig. 8. The trisected hole (Trifid-hole) in Eagle. Photo from M. Wolf of Heidelberg.]