Double Stars. 59 



double star in a galaxy field. But in a comparatively barren 

 region, and with magnitudes approaching equality, the very 

 aspect of a close pair, such as the present, is sufficient to con- 

 vey a strong impression of actual nearness, and consequent 

 physical connection, which must be the inevitable result if 

 gravity is, as we have every reason to suppose, universal. 



• This beautiful object was usually employed by Smyth as a 

 test for definition and focus, before proceeding to attack rj 

 Coronce, in those days so severe a trial both of atmospheric 

 steadiness and optical power. Of late, however, that remark- 

 able binary has become comparatively easy; the components 

 have been opening for several years, and may now be well 

 dealt with by any good telescope of moderate size. A power 

 of 170 on my 5^ inch aperture will just divide them in favour- 

 able weather; they are widely separated with 600. 



The Baron Dembowski, whose observations have just been 

 referred to, and whose labours in star-measurement are well 

 known to astronomers, has recently been increasing his optical 

 power. His former series of measures, commencing at Naples 

 ten years ago, and continued till 1858, was made with a "Dia- 

 lyte," — a peculiar construction of refracting telescope, very little 

 known in England, but of which we hope before long to give 

 an account. Since June, 1862, he has been observing with an 

 achromatic of seven French inches aperture (two inches more 

 than his previous instrument), made by Merz, the successor of 

 the celebrated Frauenhofer, and placed in an observatory at 

 Gallarate, a town of North Italy, twenty-five miles, by rail, 

 N.W. from Milan, near the end of the Lago Maggiore, and 

 commanding a view of the Alps in the distant north horizon. 

 He speaks most highly of his telescope, as enabling him to 

 measure all but the most difficult of the double stars in the 

 Dorpat Catalogue. The mode of micrometric illumination is 

 described as very efficient. Two little lamps so suspended 

 upon an axis coincident with the flame as to be vertical in all 

 positions of the instrument, give light, the one to the field, so 

 as to render the dark micrometer-threads apparent, the other 

 to the threads, making them visible in a dark field; the 

 former, however, he finds so superior that he now employs it 

 exclusively. Two concentric revolving discs intervene be- 

 tween the light and the micrometer ; one of which regulates 

 the quantity of light by its admission through openings of dif- 

 ferent sizes ; the other, divided into quadrants, changes the 

 ground of the field by interposing, at the observer's pleasure, 

 yellow, red, blue, or plain glass. The fact that the colour of 

 the field exercises considerable influence upon the visibility of 

 some objects was pointed out by Sir J. Herschel, and, in ac- 

 cordance with his suggestion, Smyth employed a red screen 



