Star-swarms, which are also characteristic features of the Galaxy, differ from star-clouds very much in the way that their name would imply—_i.e.,_ their component stars are so arranged, even when they are countless in number, that the idea of an exceedingly numerous assemblage rather than that of a cloud is impressed on the observer’s mind. In a star-swarm the separate members are distinguishable because they are either larger or nearer than the stars composing a “cloud.” A splendid example of a true star-swarm is furnished by Chi Persei, in that part of the Milky Way which runs between the constellations Perseus and Cassiopeia. This swarm is much coarser than many others, and can be seen by the naked eye. In a small telescope it appears double, as if the suns composing it had divided into two parties which keep on their way side by side, with some commingling of their members where the skirts of the two companies come in contact. Smaller than either star-clouds or star-swarms, and differing from both in their organization, are star-clusters. These, unlike the others, are found outside as well as inside the Milky Way, although they are more numerous inside its boundaries than elsewhere. The term star-cluster is sometimes applied, though improperly, to assemblages which are rather groups, such, for instance, as the Pleiades. In their most characteristic aspect star-clusters are of a globular shape—globes of suns! A famous example of a globular star-cluster, but one not included in the Milky Way, is the “Great Cluster in Hercules.” This is barely visible to the naked eye, but a small telescope shows its character, and in a large one it presents a marvelous spectacle. Photographs of such clusters are, perhaps, less effective than those of star-clouds, because the central condensation of stars in them is so great that their light becomes blended in an indistinguishable blur. The beautiful effect of the incessant play of infinitesimal rays over the apparently compact surface of the cluster, as if it were a globe of the finest frosted silver shining in an electric beam, is also lost in a photograph. Still, even to the eye looking directly at the cluster through a powerful telescope, the central part of the wonderful congregation seems almost a solid mass in which the stars are packed like the ice crystals in a snowball.