Double Stars. 189 



as may be ; remove the book, without disturbing them, and 

 they will be found very perceptibly convergent ; replace the 

 book, and the nose upon it, and they will appear parallel as 

 before. This peculiarity, which Herschel tells us was observed 

 by Bessel also, may perhaps give us a hint for the improve- 

 ment of stereoscopic vision. It seems probable that if the 

 two pictures were so arranged that their sides were not pre- 

 cisely parallel, their coincidence would be more ready, and the 

 illusion in proportion more complete. 



I have since observed (having had my attention drawn to it 

 by some of my correspondents) that with low powers there seems 

 to be a minute nebulous star or speck nearly s of the nucleus, 

 about 15" or 20" distant, which high magnifiers show as a 

 patch of light ; a denser portion apparently of the external 

 ring, between which and the nucleus the haze is less luminous. 

 Mr. Knott has remarked that Sm. has measured from the 

 nebulous star, as if it had been the brighter of the two, which 

 it certainly is not at present. 



To find this pair (for as such they are treated in the Bed- 

 ford Catalogue) we must first get B Geminorum,, which is the 

 first conspicuous star in a line from Pollux towards the Great 

 Nebula in Orion. If we then know, as we ought to do, the 

 dimensions of the field of the finder, there will be little diffi- 

 culty in turning it to a point 1° S. and rather more than 2° E. 

 of the star, when the nebula will be in the field of a low 

 power. Its place for 1860-0 is E.A.. 7 h. 20m. 54-4s.— D.N. 

 21° 11' 26-8". 



(Addendum.) Since describing in our last number, the 

 Planetary Nebula 39 $ IV., I have found that Lord Posse's 

 6-foot speculum shows it as an annulus with a wisp projecting 

 into the interior, and faint fringes all round its edge. He 

 figures the two minute stars, but takes no notice of the larger 

 one belonging to the cluster 46 M., which I still see as I saw it 

 last year, and which appears to have been seen by H. at the 

 Cape. 



DOUBLE STARS. 



Before the season passes we may add two more pairs to 

 our list. 



133. a Geminorum. 7"' 2. 196°-8. 3£ and 9. Pale white 

 and purple. Stationary, according to Sm., 1838*92. Secchi, 

 however, thinks the angle increases, having been 184°' 15 in 

 1781, and found by him 200°, 1856-107. Both with my 

 former and present telescope I have thought the large star 

 pale yellow. The companion also has appeared to me, with 

 both, very small for 9 mag. — smaller than the attendant of 



