118 



KNOWLEDGE 



[June 1, 1898. 



regions. If we assume that this density varies, from a 

 certain point O of maximum density, in the same pro- 

 portions as the cosine of the angular distance from this 

 point, then we find by least squares for the co-ordinates A 

 and D of the point il — 



From the Q A = Oh. 9 D = -I- 21° 



„ n A = 23-8 D = + 62 



Adopted co-ord. of H A = 00 D = + 42° 



The galactic latitude of this point is - 20°. 

 The agreement of the two results, found by two 

 different considerations, inter se, and with the result formerly 

 derived from nearly totally different stars, speaks strongly 

 for the reality of this centre of condensation. 



The fact alluded to in the next proposition, noted by 

 the speaker long after the above-given result had been 

 arrived at, seems to speak not less clearly in its favour. 



Sir J. Herschel, who, of all astronomers, was perhaps 

 best acquainted with the aspect of the Milky Way in its 

 whole course, says in his " Outlines of Astronomy," article 

 788, speaking of the Galaxy : " Throughout all this region 

 its brightness is very striking, and when compared with 

 that of its more northern course already traced, conveys 

 strongly the impression of greater proximity, and would 

 almost lead to a belief that our situation as spectators is 

 separated on all sides by a considerable interval from the 



dense body of stars composing the Galaxy 



within which we are excentrically situated, nearer to the 

 southern than to the northern part of its circuit." 



Prof. Kapteyn is not sure whether by " all this region " 

 is meant the whole space from the middle between A and 

 y Argus (R.A. = 8h. 5m.) and a Centauri (R.A. = 14h. 

 5m. j, or the more limited space between ry Argus (E.A. = i 

 lOh. 7m.) and the most southern point of the Galaxy 

 (R.A. = 12h. 8m.). In both cases, however, the middle 

 of this region lies near llh. 6m. of R.A. 



If, therefore, the Milky Way is to be considered as a 

 ring, and according to what has been said, and to con- 

 siderations of another order, there seems every reason for 

 the inference, then the centre is probably to be sought 

 in the direction of 28h. 6m. of R.A. 



Further, according to the investigations of Struve, the 

 sun is situated somewhat to the north of the plane of the 

 Milky Way. The centre of the Mil!{y Way, therefore, as 

 seen from the sun, must have a small southern galactic 

 latitude. The position of this centre agrees, therefore, 

 with that found for the centre of condensation of the stars 

 of the 2nd type, even within narrower limits than might 

 have been expected. 



Prop. X. The demonstration of this proposition is 

 required in order to fully complete the demonstration of 

 Prop. VI. It was attempted in several ways :— 



a. The material Stumpe-Draper gave the results em- 

 bodied in Table 10. Result :— 



94 stars of Type I., mean total p.m. = ft 0"27O, gave q = -l-0"]96 

 325 „ „ II., „ „ reduced to fi = 0"270, gave 



q = =0"166 



//. The Bradley -Draper stars with proper motions //. = 

 0"08 and 0"09 gave :— 



Type I. Tvpe II. 



Mean p.m. |x = 0"08.5 ry = -hO''0.56 (112**) ry = +0"041 (77**) 



c. (Stars of equal r). All the Bradley-Draper stars, for 

 which T 5 0"04 (Type I.), or between 0"04 and 0"29 (Type 

 II.). Only the stars of which the galactic latitude is 

 between ± 30° and ± 40° were disregarded.''^ 



* These were onlv omitted for the practical reason that tliey would 

 have had to be computed on purpose, whereas the rest served already 

 for Table 1. 



T.\BLE 11. 



(1. stars of known spectrum and of which tolerably 

 trustworthy parallaxes have been determined : — 



Mean value Number of 



of u,. Mean Mag. Mean if. Stars. 



Tvpe I. . I"(i0 2-8 0"lo9 7 



"„ ir. ... 1"(U 3 6 0"137 19 



Prop. XI. — Table 12 was obtained by bringing together 

 all the Bradley-Draper stars, with the exception only of 

 those stars of the second type of which the spectrum is 

 marked with '? in the Draper Catalogue. 



Type I. 



Type II. 



From this table, Table 13 was derived by simple inter- 

 polation. 



T.tBi.K 13. Values of q. 



qu 

 Mag. Type I. Type II. ;^j 



2-3 +0"105 +0"312 3-0 (i) 



3-3 +0064 +0-145 2 3 



4-3 +0034 +0-100 2-9 



5-3 +0031 +0092 30 



6-3 +0-027 +0-067 2-5 



Mean 2-7 



By this table the first part of the proposition is 

 demonstrated. If now we imagine the stars of the first 

 type brought down to the same distance from the sun as 

 those of the second type, then the brightness of the former 

 will be (2'7)'' = 7-3 tiines as considerable as that of the 

 latter, q. e. d. 



THE FACE OF THE SKY FOR JUNE. 



By Herbert Sadler, F.R.A.S. 



THE abnormal activity of the Sun still continues. 

 Throughout the month there is no real night, but 

 either daylight or twilight. 

 Mercury is in superior conjunction with the 

 Sun on the 5th. On the 15th lie sets at 9h. 23m. 

 P.M., or Ih. 7m. after sunset, with a northern declination 

 of 25° 10', and an apparent diameter of 5^'', yVoths of the 

 disc being illuminated. On the 25th he sets at 9h. 44m. 

 P.M., or Ih. 26m. after the Sun, with a northern declination 

 of 22° 53', and an apparent diameter of 6", yn"ntlis of the 

 disc being illuminated. On the 30th he sets at 9h. 45m. 

 P.M., or Ih. 27m. after the Sun, with a northern declination 

 of 20° 50', and an apparent diameter of 6^^", /n'Jjths of the 

 disc being illuminated. While visible he passes through 

 part of Gemini into Cancer. He is near Venus on the 

 15th. 



Venus is visible as an evening star after about the 

 middle of the month. She sets on the 15tli at 9h. 14m. 

 P.M., or 58m. after sunset, with a northern declination of 

 24° 11', and an apparent diameter of 10", Y,f.)''^s °f ^^^ 

 disc being illuminated. On the 30th she sets at 9h. 23m. 

 P.M., with a northern declination of 22° 28', and an apparent 



t In computing this table the HHcorrected proper motions have served. 



