524 Mr. W. Huggins on the Spectra 



The apparatus employed was that of which a description was 

 given at page 415. A second eyepiece was used in these obser- 

 vations, having a magnifying- power of nine diameters. For the 

 greater part of the following observations on the nebulas, the 

 cylindrical lens is not necessary, and was removed from the in- 

 strument. The numbers and descriptions of the nebula?, and 

 their places for the epoch 1860, January 0, included within 

 brackets, are taken from the last Catalogue of Sir John Herschel*. 



[No. 4373. 37H.IV. R.A. 17H8 m 20 s . N.P.D.23°22'9"-5. 



A planetary nebula; very bright; pretty small; suddenly 

 brighter in the middle, very small nucleus.] In Draco. 



On August 29, 1864, 1 directed the telescope armed with the 

 spectrum-apparatus to this nebula. At first I suspected some 

 derangement of the instrument had taken place ; for no spec- 

 trum was seen, but only a short line of light perpendicular to 

 the direction of dispersion. I then found that the light of this 

 nebula, unlike any other ex-terrestrial light which had yet been 

 subjected by me to prismatic analysis, was not composed of light 

 of different refrangibilities, and therefore could not form a spec- 

 trum. A great part of the light from this nebula is monochro- 

 matic, and after passing through the prisms remains concentrated 

 in a bright line occupying in the instrument the position of that 

 part of the spectrum to which its light corresponds in refrangi- 

 bility. A more careful examination with a narrower slit, how- 

 ever, showed that, a little more refrangible than the bright line, 

 and separated from it by a dark interval, a narrower and much 

 fainter line occurs. Beyond this, again, at about three times 

 the distance of the second line, a third exceedingly faint line was 

 seen. The positions of these lines in the spectrum were deter- 

 mined by a simultaneous comparison of them in the instrument 

 with the spectrum of the induction spark taken between elec- 

 trodes of magnesium. The strongest line coincides in posi- 

 tion with the brightest of the air lines. This line is due to ni- 

 trogen, and occurs in the spectrum about midway between b and 

 E of the solar spectrum. Its position is seen in Plate VI. t 



The faintest of the lines of the nebula agrees in position with 

 the line of hydrogen corresponding to Frauhhofer's F. The 

 other bright line was compared with the strong line of barium 

 2075 % : this line is a little more refrangible than that belonging 

 to the nebula. 



Besides these lines, an exceedingly faint spectrum was just 

 perceived for a short distance on both sides of the group of bright 



* Philosophical Transactions, Part I. 1864, pp. 1-137. 



t See also Philosophical Transactions, 1864, p. 156, and plate 1. 



% Ibid. p. 156. 



