dividual stars are so faint that the most powerful instruments scarcely suffice to bring them out. One of the most remarkable clusters in the northern heavens is that of Hercules. To the naked eye it is but a faint and insignificant patch which would be noticed only by a careful observer. But in a large telescope it is seen to be one of the most interesting objects in the heavens. Near the border the individual stars can be readily distinguished. But they grow continually thicker toward the center, where, even in a telescope of two feet aperture, the
Fig. 7. The Cluster ω Centauri, Photographed by Gill at the Cape Observatory.
observer can see only a patch of light, which is, however, as he scans it, suggestive of the countless stars that must there be collected. By the aid of photography, Professor Pickering has nearly succeeded in the complete resolution of this cluster.
In many cases the central portions of these objects are so condensed that they cannot be visually resolved into their separate stars, even with the most powerful telescopes. . A closer approach to complete resolution has been made by photography. We present copies of several photographs which have been made by Pickering, Gill and others.
