I04 



KNOWLEDGE & SCIENTIFIC NEWS. 



[May, 1905. 



of two plans, otherwise equal, that one will be best which, 

 on a given scale, and with a given number of maps, 

 makes the maps cover the least possible area. It is also 

 obvious that the distortion and scale variation of a map 

 should be as small as possible." He also says " There 

 is only one plan according to which such an atlas can be 

 constructed so as to satisfy even the chief requisites 

 which Star Charts are intended to meet." If the maps 

 are to be of equal size and shape, the surface of the 

 sphere must be approximated by a solid figure com- 

 posed of a number of faces each forming a polygon. 

 But of these the most suitable is the dodecahedron, or 

 solid figure composed of twelve pentagons. From the 

 figure it will be evident how each one of the pentagons, 



though forming a flat plane, will not require that the 

 position of the objects depicted upon them will be much 

 distorted from those on the surface of a sphere. It will 

 be noticed that the distortion is greatest in the angles of 

 the pentagons, so if a circle be circumscribed around the 

 pentagon, the distortion of those part* outside the penta- 

 gon will be no greater than those in the angles, and the 

 circle will practically occupy no greater space of paper 

 than the pentagon. By adopting the circle instead of the 

 pentagon we also obtain another important feature, and 

 that is the overlapping of the adjacent maps. In these 

 12 maps one-fifth of the hea\ens is included in the over- 

 laps. Occasionally stars lying near, but outside, the 

 border are shown, so as to complete the principal mem- 

 bers of a constellation. 



Having decided upon this system, the ne.xt question 

 was as to the colouring and mode of representing the 

 stars. Most maps mark the stars in black on a lighter 

 ground, the opposite to Nature, and causing much con- 

 fusion with letters and signs. White stars on a blue 

 ground have therefore been adopted. 



The names of the constellations are here put in large 

 letters, so arranged as to cover as far as possible the con- 

 stellation, and yet being so placed as not to interfere with 

 the individual stars. The lines of R.A. are only given for 

 the hours, though around the border divisions are put 

 corresponding to each ten minutes, and Declination lines 

 are put at each 5 degrees. 



As regards the nomenclature of the stars, we have 

 added names to all those mentioned in the Comte de 

 Miremont's Popular Star Maps, the Greek letters to those 

 recognised by such, and I-'lamsteed's numbers to others. 

 There remain many other smaller stars, which bear various 

 numbers according to different catalogues, but we have 

 thought it best to leave them unnamed, as otherwise con 

 fusion may be caused. 



The brilliancy of the stars, known by the misleading 

 designation of " magnitudes," but which, of course, has 

 nothing to do with the actual size of the stars, are here 

 given according to conventional shapes (as shown on each 

 sheet). The actual si/.e represented varies slightly, since 

 the stars are not, as a rule, of any txaci magnitude. These 

 are entered in accordance with the Harvaid I'hotometry. 



The Milky Way has been added in a manner which 



may not perhaps appear wholly satisfactory, but it be- 

 comes a practical difficulty to depict that which is but a 

 mass of stars in such a way as to interfere as little as 

 possible with stars superposed upon it. Many other 

 practical difficulties have appeared during the construc- 

 tion and printing of the first map, but in future we pro- 

 pose to employ a slightly different system, which should 

 secure greater clearness and accuracy. 



MAP I. 



North Polar Stars. 



This is perhaps the most important map of the whole 

 series for several reasons. All the stars here represented 

 are always above the horizon in England. One of the 

 chief practical uses in a knowledge of the position of the 

 stars is to be able to ascertain the direction of true north. 

 l>y becoming conversant with the lie of the chief stars 

 in tliis region the north point is readily noted. Besides 

 these this map happens to include several of the most 

 conspicuous and easily remembered constellations in the 

 heavens, viz., the Great Bear, the Little Bear, and 

 Cassiopeia. 



It may be almost superfluous to mention that the North 

 Pole of the heavens is found by prolonging the line of the 

 " pointers " (jt and 0. Ursa Majoris) towards Polaris, which 

 star stands very much alone, and close to the Pole. If 

 Polaris be joined by an imaginary line to the end of the 

 "tail" of the Great Bear (-n) the Pole will be approxi- 

 mately where these two lines cross. 



Among the more noteworthy stars and other interest- 

 ing objects to be found in this map are the following : — 



Cephei {2 ih. 2^m. + 5/' 54')- Double. The princi- 

 pal star is variable from 3-7 to 4-9 magnitude, and is a 

 spectroscopic binary of great interest. The variability, 

 in this case, is proved not to be dependent on eclipse 

 obscuration with a darker body, but seems to be due to 

 an actual variation in radiating power. 



o Cassiopeia (oh. 34m. + 53' 59') is a quadrupal and 

 irregular variable ranging from 2-2 to 2'8 mag. 



V Cassiopeia (oh. 43m. -|- 57" 17'). A binary, the two 

 stars being of 3-5 and 7-5 magnitudes respectively, at a 

 distance apart of 5"-b8. 



a Cassiopeia (23h. 54m. + 55° 12'). A double star, one 

 white, of the 5th magnitude, the other blue of 7-5 magni- 

 tude. Distance apart 3"-o. 



Perseus, between 9 and 5 are two clusters. Near this 

 point a Nova was discovered in 1895, of the 9th magni- 

 tude. 



a Ursa Minoris, "Polaris" (ih. 23m. -f 88" 46'). 

 Mag. 2-12. This is a double star, the smaller one at a 

 distance of 19" being of 9th magnitude. The larger star 

 is a spectroscopic binary, period 4 days, probably having 

 two dark companion stars. 



In Ursa Major close to ji is situated the " Owl Nebula " 

 (iih. gm. + 55' 34') invisible to the naked eye, but by 

 aid of powerful telescopes is seen to consist of two spirals 

 formed in opposite directions. 



(Ursa Majiiris, "Mizar" (i3h. 20m. + 55" 26'). A 

 well-known double star, magnitude 2-i and 4-2, distance 

 apart J4"'4- Position angle i47""4. The larger star is a 

 spectroscopic binary of two bright and equal components. 

 "Alcor," 5th magnitude, is ii" away from (. 



Draco. A gaseous nebula, of a pale blue colour, lies 

 close to the north pole of the ecliptic. (i7h. 59m. + 

 66'^ 38'). 



From a point in Perseus dh. om. -f 57'"') come the 

 well-known Perseids, or meteor showers, about the 9th- 

 iith of August. 



