MOUNT WILSON SOLAR OBSERVATORY. I97 



on Cramer isochromatic plates. The results were satisfactory when the 

 steadiness of the air was such as to permit of this enlargement. A photo- 

 graph of Saturn, made in this way on November 19, is reproduced as Plate 

 4. The original negative shows the belt, polar caps, and rings very well de- 

 fined. The Cassini division is strongly shown and feeble traces of the 

 Encke division appear. The exposures were ordinarily from 10 to 12 sec- 

 onds. One exposure of 40 seconds shows the crape ring fairly well, though 

 the rest of the planet is of course overexposed in this case. 



The photographs of Mars, which were made through a red screen on 

 Seed Process plates, stained with a red sensitizing dye, are not so successful 

 as those of Saturn, but are perhaps as good as could be expected under the 

 circumstances. Though some of them show much detail, they are not as 

 sharp as photographs taken in 1909 with the same instrument. On some 

 of the negatives, however, a great deal of broken detail is shown in the 

 region of Mare Cimmerium. The Solis Lacus region was photographed 

 less satisfactorily. The telescope was not available for this work on any 

 good night when the Syrtis Major region was visible. 



In addition to the photographic work, some visual observations were 

 made which were of the highest interest. Professor Barnard states that 

 for some reason which he can not clearly explain, though it was perhaps 

 due to an early observation with a reflecting telescope under unfavorable 

 conditions, he had formed the idea that the reflector would not be satisfac- 

 tory for visual work. This idea had been more or less corrected by a brief 

 view of Saturn at the time of the meeting of the Solar Union in August 

 19 10, which had impressed him very favorably, with the 60-inch telescope. 

 The observations of Mars, however, fully convinced him of the suitability 

 of the 60-inch reflector for visual work, and in many respects they proved 

 to be superior to those made with large refracting telescopes. The principal 

 reason for this was the remarkable purity of the image and freedom from 

 color in the reflector, which is due to the entire absence of the secondary 

 spectrum. Compared with the images of Saturn and Mars in the 60-inch, 

 those in a refracting telescope have a muddy or dirty look. This was per- 

 haps more striking in the case of Mars than in that of Saturn. Mars was 

 almost colorless. There was a slight pinkish tinge to the image, giving one 

 the impression of a globe whose entire surface had been tinted a slight pink 

 color on which the dark details had been painted with a grayish colored 

 paint, supplied with a very poor brush, producing a shredded or streaky 

 and wispy effect in the darker regions. In the visual observations there 

 was a better chance than in the case of the photographic work, for one 

 could pick out moments of steadiness that would be lost to him during the 

 exposures. The results in the case of Mars are said by Professor Barnard 

 to be quite beyond his power of either describing or depicting. An artist 

 could have studied the planet and given a representation of the structural 

 details shown in the dark regions that would have conveyed some idea of 



