Satellites of tlie Mercury Lines. 447 



About these last two there is absolutely no question. 

 Gale and Lemon found them, and I have repeatedly seen 

 them as a single line very close to the main line with a 

 low-power spectroscope (plane grating and lens of 1-metre 

 focus). I never regarded this companion line of the yellow 

 line as a satellite, and was surprised to find it so close to the 

 satellite group with the 42-foot spectrograph. There is on 

 the plate perhaps a faint suggestion of the satellite at 

 + *082, but I should want to take another photograph with 

 a longer exposure before being sure of it. No trace appears 

 of the fainter components given by Lunelund, and I am 

 surprised to find that he does not include the close pair well 

 to the left of the group in his list of lines the existence of: 

 which is established, for the photograph published by Gale 

 and Lemon established their reality beyond question. 



The 5461 Green Line. 



The spectrograph was not giving its best definition on the 

 evening on which this photograph was taken, on account of a 

 high wind, and the resolution is no better than the one made 

 by Gale and Lemon. I have only to record the discovery of 

 a broad faint band on the short wave-length side of the 

 satellite at — *233. The edges of the band are at — "327 and 

 — "414. It is very distinct on the original plate, but has lost 

 much in the process of enlargement, and as it may vanish 

 entirely in the reproduction I have retouched it in the upper 

 half of the picture (fig. 3, PL IV.). No trace of this has 

 been found by any previous observer, but there is no doubt 

 about its existence. 



The 4359 Violet Line. 



This line was photographed in both the fourth and fifth 

 orders. The fourth order showed the middle line double, 

 a sharp narrow line to the left and a broad one to the right. 

 The fifth order divided the broad component into two, the 

 middle line being resolved into a triplet. I believe that it 

 is still more complex. This photograph is reproduced in 

 fig. 4 (PI. IV.), print a being made darker than b to bring- 

 out the division of the middle line. The superior resolving 

 power of the grating is well shown by comparing this 

 picture with the one made by Gale and Lemon. I suspect 

 that some of their trouble arose from vibrations and strise 

 due to air currents, for their photograph made in the fifth 

 order does not appear to show any greater resolving Ijjower 



