446 Prof. P. W. Wood on the 



make the instrument equal in resolving power that of the 

 largest interference spectroscope, and at the same time fur- 

 nish results about which there will be no ambiguity. "We 

 will now consider the results obtained in the case of the four 

 lines which I have already investigated. 



The 5769 Yellow Line. 



A photograph of this line made in the fourth order is 

 reproduced in fig. 1 (PL IV.) . I have indicated the middle of 

 the main line in each case with an ink dot. The positions of 

 the satellites are as follows : — 



+ •042 



Main line. 

 -•055 

 -•112 



An inspection of the photograph is sufficient to convince us 

 that all of these satellites are real, and yet the one to the left 

 (•112) was missed by Gale and Lemon, as well as by all of the 

 other observers except Lunelund, who gives it the same value 

 (•112), and Janicki, who placed it at '113. Nagaoka records 

 a satellite at —"109, which may be identified with it, but his 

 photographs indicate the presence of so many false lines and 

 ghosts that it is difficult to be very sure of anything. I 

 cannot understand why the Michelson grating failed to record 

 it, though, as I have already stated, the use of the tube 

 " end-on " intensifies many of the fainter companion lines. 

 Lunelund's other values agree very well with those given 

 above, though I find no trace whatever of the satellites 

 + •084 and + '121, which he regards as probably real. He 

 gives their intensities as about one-half that of the one 

 at —'112 ; yet the most careful scrutiny of my photograph 

 fails to reveal the slightest trace of them, though — *112 is fully 

 four times as black as the minimum visible on a photographic 

 plate. I feel therefore quite certain that these satellites are 

 spurious. 



The 5790 Yellow Line. 



This line is shown by fig. 2 (PI. IV.), and the satellites 

 are as follows : — 



+ •222 

 + •164 

 + •131 



Main line. 

 -•124 

 -•191 

 and two lines at — -914 and —1-007. 



