14^ 



KNOWLEDGE & SCIENTIFIC NEWS. 



[July. 1905. 



In my " Road-Book to the Stars " I asked for correc- 

 tions and additional data. Mr. Gore kindly sent mc 

 the paper on the " Relative Brightness of Stars," 

 which he communicated (January, 1905) to the Royal 

 Astronomical Society. In this he only gives stars for 

 which he thinks the parallaxes are fairly good; those 

 mcst reliable he marks (*), whereas in my "Road-Book" 

 I gave all the estimates I could collect. So far as Mr. 

 Gore's list goes my distances agree with his; I have 

 now in the list for ist magnitude stars herewith put (*) 

 to the distances he considers most reliable, and (?) 

 against those he does not give at all. Otherwise the 

 light-years remain as in my book. Mr. Gore has taken 

 the Sun's magnitude as - 26.5, whereas I took if as 

 - 2(-).^; so that, other things being equal, where he 

 called the relative brightness of a star 1,000, I should 

 call its sun-power 1,095. 



Mr. O. R. Walkey also has .sent me a long and very 

 interesting account of his method of getting at the 

 .\bsiilule Parallaxes for ;ill the ist magnitude and 

 some other stars. Onlv he himself could do jitsticc to 

 his method, but I give his absolute parallaxes and sun- 

 pf)wers. (He takes the .Sun's magnitude as — 26. .4.) If 

 Canopus is, as he thinks, of 71,8^0 sun-powers, and if 

 the surface brightness is the same as the .Sun's, the 

 -Sun might be situate at the centre of Canopus, the 

 earth would revolve about 22 million miles below its 

 surface, and we should find it quite unpleasantly hot. 



In the following list I have divided the first magni- 

 tude stars into two classes : the first, Orion, tvpe O, 

 Sirian, type I, and Procyon, type I-II. The second, 

 Solar, type II, and .Autarean, type III. Parallaxes ob- 

 served at the Cape are marked C, at Yale, Y. The 

 magnitudes arc revised Harvard. 



In the Appendix to my " Road-Book to the Stars " I 

 give all the data as to other magnitudes I could collect, 

 but they are too few to enable me to work out, 

 correctly, the average distances and sun-power for each 

 type and magnitude. ICstimates may, however, be 

 made from Professor Kapteyn's formula derived from 

 parallactic motions. Professor Xcwcomb has done this 

 in his book on the ".Stars," doubling the di.stance 

 everv two magnitudes, but Mr. O. R. W'alkcy has 

 corrected his parallaxes bv going carefullv through 

 Kapteyn's original work. From these corrected 

 parallaxes I have worked out the distance in light-years 

 :md the sim-power for each type and magnitude. T/ie 

 rt'Siif/s, if they can Ix relied upon as averages (not, of 

 course, for individual stars), are of great importance. 



for the first magnitude we 

 )()5 for type 1, and 529/397 

 for type II. I'"ar beyond the second magnitude ! From 

 the second down the sun-power is halved everv two 

 magnitudes — tlie further we go the smaller is the average 

 size/ But in my " New X'iew of the Stars " I show 

 that in the only space-sphere thoroughly surveyed, the 

 pcrcciil;i.^i s are as follows: — :?.( of [ to 56 sun- 



Type. Masnitude, Parallax 



'Rflntivc ! 



Error. 

 ± 



My ■■ Koad.Book. 



Mr. VValkey's Kstimates for 



Mr. Gore's 



Relative 1 ] 



Light- Sun- Brightness. Absolute i Light- Sun- 



Years. Power. Parallax. , Years. Power 



Sirius I - ''58 



Canopus Ill - o-!S6 



Vega I -j- 0-14 



Rigel 0-34 



Procyon I-II 0-48 



Achernar () o'6o 



ft Centauri O 0-86 



.-Mtair I o'Sg 



a Criicis () i'05 



Spicn O I '2 1 



Foinalhant I rag 



oCyKni . . I 133 



Kegiiliis . . ( ) 1-34 



fl Criicis ( ) I '50 



First Class 14 Stars a veraRe o'5o 



•370 

 •000 

 •082 

 •000 



■334 

 ■043 

 •030 

 •232 

 •050 

 •000 

 •130 



Y — -012 



Y -024 

 C '000 



•02191 -015 



3132 



8965 



a Centanri 



Arctiirii 



Capell.i 



BctelRiiese 



Aldebaraii 

 Pollux . 

 .•\nlar(~ 



SL'cond CI. I 



148() 



. 7 .St;ir.s .ivt-r.-i^f; 



N.B. Some of my sun-powers i narkeil a) arc slightly altered from Uiose n'ven belore owing lo corrected magnitudes. 



