12 EDWARD EMERSON BARNARD— FROST [toMO, ™[vouxxi; 



which might otherwise have been lost. A firm of commercial photographers in Chicago, A. 

 Copelin & Son, personally well known to Mr. Barnard, undertook the task of making the neces- 

 sary number of 700 prints from each of the 50 negatives selected to represent the Galaxy. For 

 two years, beginning in May, 1915, Mr. Barnard made frequent trips to the city, and personally 

 inspected each of the 35,000 prints, rejecting hundreds and even thousands of those which 

 seemed to him to be lacking, in some detail, the high quality of excellence which he desired. 



It was very difficult for Mr. Barnard to take time from the reduction and discussion of cur- 

 rent observations in order to devote himself to the descriptions which were to accompany the 

 photographs. He was also constantly finding new points of interest, as he studied each photo- 

 graph in detail, which led him to desire new photographs centering on special regions, or having 

 longer exposures than he had previously given. The publication of this Atlas was accordingly 

 delayed, but, fortunately, Mr. Barnard had been prevailed upon to give more time to the com- 

 pletion of the text, and it had been finished, so far as the 50 regions illustrated were concerned. 

 It is to be regretted that he had not written the introduction, which would have summed up his 

 views on the structure of the Milky Way, based upon a personal knowledge more intimate than 

 that possessed by any other person. His notes on the introduction are fragmentary, but they 

 can be used, and it is hoped that the Atlas can be published during 1926, in essentially the man- 

 ner in which Mr. Barnard would have desired it, and accompanied by charts from drawings 

 giving the coordinates of the region of each photograph, with a designation of the important 

 features. 



During the last decade, Mr. Barnard had taken a special interest in the dark markings in 

 the Milky Way. At first he called them vacancies, and it was only gradually that he was led 

 to the view that they were, after all, in many instances, dark objects projected against the 

 Milky Way and absorbing its fight. The titles of some of his papers show this gradual transi- 

 tion in the interpretation of these extraordinary structures. 



In his paper entitled "Some of the dark markings of the sky and what they suggest," 

 Astrophysical Journal, 43: 1-8, 1916, he says: 



An important fact that may come from our knowledge of the existence of dark nebulae is that their masses 

 must be much greater than would be assumed for the ordinary nebulae, because they are perfectly opaque and 

 must berelatively dense, and hence comparatively massive. If this is so, then we must take into account these 

 great masses in a study of the motions of the stars as a whole. 



In that paper he placed side by side a luminous gaseous nebula and a dark object of very 

 nearly the same shape: the resemblance is striking. 



One of his most notable papers, "On the dark markings of the sky, with a catalogue of 1S2 

 such objects," published in the Astrophysical Journal in 1919, summed up his studies of these 

 objects, which will doubtless be designated in the future by the numbers which he assigned to 

 them in the catalogue. 



A very important question in recent years has been the proper location in our stellar system 

 of the globular star clusters. From his studies of their appearance on his photographs of the 

 Milky Way, Professor Barnard was led to the opinion that the clusters are in some instances 

 obviously projected against the background of the Milky Way. To show his ideas as to the 

 relative distances of some clusters and the Milky Way, we may quote from a short note pub- 

 lished in the Astronomical Journal in 1920: 



Just as the great star clouds of the Milky Way act as a background against which non-luminous masses 

 may be seen in dark relief, they must act also as a screen and thus hide any object that is behind them. This 

 gives us a means of inferring the relative distances, etc., of many of the great globular clusters. The rich regions 

 of Sagittarius and Aquila, in which some of the finest globular clusters occur, are specially remarkable for their 

 density. That these clusters are nearer than the great star clouds is evident, for they would not be seen through 

 the star clouds if beyond them. 



He cites as particular examples, N. G. C. Nos. 6266 (M 62), 6273 (M 19), 6293, 6304, 6333 

 (M 9), 6528, 6656 (M 22), and 6712. 



Although Professor Barnard had given great attention to the surface markings of the 

 planets, it was not until 1905 that he began experiments in photographing the planets with the 



