OP ARTS AND SCIENCES. 



407 



Investigations on Light and IIeat, made and published wholly oe m part wrrn 

 Appropriation from the Rcmford Fund. 



XVIII. 



A PHOTOGRAPHIC STUDY OF THE NEBULA OF 



ORION. 



By Edward C. Pickering. 



Presented March 11, 1885. 



No portion of the heavens has been more carefully studied than that 

 containing the Nebula of Orion. The monographs by Prof. G. P. Bond 

 (Annals Harvard College Observatory, V.) and by Prof . E. S. Holden 

 (Washington Astronomical Observations for 1878, Appendix I.) show 

 the vast amount of material collected by eye observations. For a pho- 

 tographic study of the same region the following specimens are in the 

 photographic collection of tlie Harvard College Observatory : — 



A. Artotype enlargement of the first photograph of the nebula taken 

 by Dr, Henry Draper, September 30, 1880. Exposure, 51 minutes. 



B. Artotype enlargement of a photograph taken by Dr. Henry Dra- 

 per, March 11, 1881. Exposure, 106 minutes. 



C. The original negative taken by Dr. Henry Draper on March 14, 

 1882. Exposure, 136 minutes. This negative, except for a slight pho- 

 tographic blemish, is nearly identical with that from which D. was taken. 



D. An enlarged glass positive of the second photograph taken by 

 Dr. Henry Draper, March 14, 1882. Exposure, 137 minutes. This 

 positive is a duplicate of that employed in making the paper prints, E. 

 The two positives were taken, and any objects resembling stars, but 

 not found on both, were assumed to be defects, and were painted out 

 of the other positive by Dr. Draper. 



E. Several artotype enlargements of the second photograph, taken 

 IMarch 14, 1882, by Dr. Henry Draper. 



F. Carbon print of photograph taken by Mr. Common with his .3-foot 

 redactor, January 30, 1883. Exposure, 39 minutes. Enlargement 

 about 7 times. 



G. Glass positive, — a direct copy of the negative taken by Mr. 

 Common with his 3-foot reflector, February 26, 1883. Exposure, 60 

 minutes. 



