522 



Chronicles of Science. 



[Oct., 



dividually through increase of distance, before their distances from 

 each other became evanescent, the group (or the special order of 

 stars considered — as the case may be) could not possibly present a 

 nebulous appearance, at any stage of its recession, with whatever 

 telescopic power it was studied. On the other hand, if the distances 

 between the stars became evanescent before the stars vanished in- 

 dividually, the group or order of stars must necessarily become 

 nebulous when it reached a certain distance. In the case of a 

 group consisting of several orders of stars, one order might thus 

 become nebulous at a certain distance, but with yet greater increase 

 of distance this nebulosity would vanish, and the question whether 

 any new nebulosity would replace it would depend wholly on the 

 question whether the next higher orders of stars belonged to one 

 or other of the classes considered above. Considerations thus ap- 

 plied to a group of stars passing away from the eye, may obviously 

 be extended to star-groups at various distances ; and since we could 

 not judge of the distance of the moving group from its resolvability 

 or irresolvability, so neither can we place any reliance on those 

 estimates of the distances of nebulas which have been founded on 

 their resolution. 



Mr. Williams describes some early telescopes made by Giuseppe 

 Campani which he purchased at the sale of the late Dr. Lee's in- 

 struments. Eeaders of the ' Celestial Cycle ' and its ' Prolegomena ' 

 will not need to be reminded that these instruments were tested by 

 the late Admiral Smyth. 



Mr. Powell communicates a paper " On the Double Star a 

 Centauri." The companion has recently reached its lesser maximum 

 of distance, and has commenced its return towards the primary. 

 Thus an exactitude of determination has become possible, which 

 (as Captain Jacob used to remark) was impossible while it remained 

 unknown how far the companion would pursue its northerly ex- 

 cursion. The following are the elements which Mr. Powell now 

 assigns to the orbit : — 



Semi-axis 



20" -13 



Period 



76-25 



Periastral passage 



. 1871-2 



Longitude of periaster . . 38° ■ 40 



Eccentricity -63944 



Kising node 24° -18 



Inclination 81° '13 



These results differ somewhat importantly from those obtained by 

 Sir John Herschel, Hind, and formerly by Mr. Powell himself. 



Mr. Seabroke endeavours to show that Mr. Lockyer's theory 

 that the corona is a phenomenon of the earth's atmosphere " is quite 

 possible." For this purpose he considers how far such spectroscopic 

 results as Major Tennant obtained during the Indian eclipse, might 

 be accounted for on that theory. It is unfortunate that in place of 

 dealing with the actual circumstances of that eclipse, Mr. Seacombe 

 determines " what spectrum we ought to obtain from a corona at 



