1 70 Transactions. — Miscellaneous. 



The blue Planetary Nebula near the Southern Cross. — This object, 

 No. 3365 in Sir John Herschel's Catalogue, is in E. A. llhrs. 44min., and 

 decl. 5^° 31' S. The colour of this strange object is a bright unmistakable 

 blue. This nebula, like other planetary nebulse that have been examined 

 in the Northern Hemisphere, gives a spectrum of one bright luie. Possibly, 

 in a larger instrument, more lines might be seen. It is, of course, 

 impossible with my apparatus to determine the position of this line, as 

 there are no landmarks, so to speak, to guide one to a decision. It is most 

 probable, however, that it is one of the hydrogen or of the nitrogen lines, 

 and that this planetary nebula is a spherical mass of one or both these 

 gases in an incandescent state. 



a Crucis. — This superb ■pair of stars, by far the finest in the sky, con- 

 sists of two stars, bluish white in tint, and very nearly equal in size, each 

 being of the second magnitude. There is a distant six-magnitude com- 

 panion, of a sea-green colour, as well as three smaller comites of magni- 

 tudes, 12^, 14, and 18 respectively. These latter are well seen in the Sc- 

 inch reflector, but a small telescope of course does not show them. I have 

 made a very great number of measures of the angle of position of this star, 

 and having weighted the observations with reference to the state of the 

 atmosphere, etc., at the time when the measures were taken, I find the 

 angle of position for the year 1878-7 to be 118*5°. This, by a very singular 

 coincidence, is exactly the same angle as that obtained by Powell in the 

 year 1863. Herschel gives the angle for 1835-83 as 120*6°. I may say 

 that, if I had rejected two of my observations, which were made in rather 

 bad weather, and which exceeded the average of the rest by 1^° and 8^° 

 respectively, the angle obtained, taken in connection with Powell's and Sk- 

 John Herschel's, would have indicated, I believe, a very slow but really 

 regular angular motion, in a retrograde direction, since Herschel's time, 

 and would, with the measures of distance given below, have convinced me, 

 at all events, that a Crucis is a binary star of very long period. The temp- 

 tation ui such cases to " cook one's accounts" a little, to omit taking into 

 account facts or numbers which do not square with one's own views or 

 wishes, is very strong, but the man who cannot resist it had better give up 

 science altogether and take to something else in which it is not of vital 

 importance that he should tell the truth, the whole truth, and nothing but 

 the truth, with regard to his observations. The distance between the two 

 stars at the epoch, 1886-36, was 5*65"; in 1863, Powell made it 4-98"; and 

 at the end of last month, 1879*75, the distance, a mean of several measures, 

 was 4-79". a Crucis is a hydrogen star, but its spectrum is very difiicult to 

 observe, except in the finest weather. Even then the only lines that I can 

 make out are the hydrogen lines, and they are by no means very easy to see. 



