156 



KNOWLEDGE. 



[July, 1902. 



Perseu!", imd ])ro-c'ininentlj a inaxiintiiii very largo uiul 

 jironouuccd whose centiv falls in Cvgnus and which 

 sin'cads oviT Cassiopeia and Aquila. Outside the Milky 

 \Vav tho density of ArLjclauder stars, taken as a whole, 

 does not attain to any maximum. 



It is worthy of notice that so loni; as it concerns the 

 relatively bright stars — by comjiansou with the minute 

 stars which especially ]>roduce the optical phenomenon of 

 the Milky Way — the naked eye perceives nothing of the 

 condensations that I have indicated here. The stars visible 

 to the naked eye grou]> themselves especially round Orion 

 and Argo in a zone which makes an angle of 20 degrees 

 with the Milky Way — "the belt of bright stars " recognised 

 and described bv Sir John Herschel. 



In a second article I will compare the results obtained 

 by Seeliger and Stratonoff, with researches of another 

 order, to draw from them some conclusions on the subject 

 which is now occupying us. 



THE "AMERICA" NEBULA IN CYGNUS. 



By Di-. Mas Wolf. 



Herschel records an exceedingly faint and very extended 

 nebulosity in this place. On the 12th of December, 1890, 

 working with a 5-inch Kriinz photographic doublet, I 

 discovered here a very fine and interesting nebula of 

 enormous dimensions, and very bright photographically. 

 As the outlines of the nebula almost exactly resembled 

 those of North America ou the map, I called it the 

 "America" nebula. I published a picture of it in 

 Knowledge for July, 1892. Last year I succeeded 

 in obtaining a photograph of it with my two 16-inch 

 Brashear portrait lenses. The photograph of the two 

 which is otherwise the better has a defect near the middle 

 of the ]>late ; the accompanying reproduction is therefore 

 from the other one. Although it is from the worse 

 negative of the two, it is a very interesting picture, and 

 shows very well the unrivalled beauty of the " finest nebula 

 of the sky." The extent of the nebula from north to 

 south is in all more than three degrees- The bright 

 nebulous star on the right hand (the west) is the star 

 f Cygni, and many interesting arms and wings of 

 nebulosity radiate from it. 



The centre of the "America" nebula has the co- 

 ordinates : — 



R.A. = 20h. 54m. Dec. = 43° 45' (1855-0). 



The jdate was by Schleussner ; it was exposed for four 

 and three-quarter hours in all on the evenings of July 

 12th and 13th, 1901. Scale one degree equals about 

 eight centimetres. 



Heidelburtj. 



♦^ 



THE USE OF HAND TELESCOPES IN 

 ASTRONOMY. 



By Cecil Jackson. 



IV.— THE STARS. 



I will now describe a few objects within the reach of 

 hand telcsco]>es not exceeding two inches in apcrtm-e. 

 One of the most striking double stai's visible in a li or 

 2-inch telescope is Mizar (denoted in stai--maps by the 

 Greek letter ?), in Charles's Wain, or the Great Bear. 



Fig. 9 shows tho position of Mizar in Chai-les's Wain. 

 There is also another beaiitiful double stai- in the ad- 

 joining constellation of Canes Venatici. It is marked 

 Cor Cai'oli in Fig. 9. One of the stars of this double 

 is a beautiful blue, or blue-grccn. It is a notable fact 



tliat if o!ic of the stars of a double is blue the star of 

 this colour is the smaller of the two. 



Fig. 10 sliows Mizar, as seen with my Ijl-inch telescope 



on Sept. 3, 1892. An astronomical eye-piece of fairly 

 low power was used on tho instrument. A power of 

 thirty or thii-ty-five will readily divide this double star. 



Fig. 11 shows the chief stai-s in Orion, as well as the 

 position of the Great Nebula. This constellation is vc)-y 

 easily recognised in the southern sky dui'ing the winter 

 mouths. The Nebula can be seen with a pocket telescope 

 on a dark night. 



Fig. 12 gives some idea of the Orion Nebula, as seen 

 in my l|-inch telescope with its own terrestrial eye- 

 piece set to magnif}^ 25 diameters. This sketch was 



Fis. 11. Fig. 12. 



made at about 51i. 55m. p.m., Jan. 17, 1900. There 

 are many stai-s near the Nebula, some of which are 

 shown in this sketch. The pair A is worthy of notice. 

 The group X is remarkable as seen in the telescope, 

 being then seen to be a triangle composed of three 

 stai-s. There are also many smaller stars visible in the 

 field of view. Tho stai- Betelgeuze (a) is noticeable as 



Fig. VA. Fig. 1 I. 



being a i-eddish star, while the star Rigcl (/3) is a 

 brilliant white. 



Another double star visible in a small telescope is 

 /8 Cygni. Its jiositioii in the Cross in the constellation 



