This second part of the Atlas has been provided to aid in the convenient use and study of the photographs contained in Part I, for reasons which were stated in notes by Professor Barnard as follows:

When comparing astronomical photographs made with long exposures with star charts I have frequently had much trouble through the want of an approximate position, in identifying stars and other objects on the photographs. Also, very often, the colors of the stars so change their relative intensities that they are not easily recognized on the chart. The photographs in the present work are intended as pictures of the sky and it would have been impossible to mark co-ordinates on them without spoiling their pictorial value. It was therefore decided to make a map, with co-ordinates, corresponding to each photograph and on the same scale. Though this has required much work, the charts assist greatly in the approximate location of any object shown on the photographs. They have been of great service to me in studying the photographs and I believe will be a welcome addition to the Atlas.

The photographs are not all enlarged in the same proportion, and therefore are not uniform in scale. All of the fainter stars shown on the Durchmusterung charts were not put on the diagrams, but it is believed enough of them are given to permit a ready identification of objects in any part of a photograph. Four stars on each photograph, located near the corners, were identified and used for determining its scale and for locating the system of co-ordinate lines. The epoch 1875.0 was adopted and is used throughout this work.