THE FIXED STARS. 5 n 



Argelander's gauges show the same concentration in telescopic stars 

 brighter than the tenth magnitude, and it is even more plainly to be 

 made out from Mr. Proctor's chart of his great catalogue. If parallel 

 to the great circle of the Milky Way two small circles be passed, each 

 at a distance from it of 30, having between them a broad belt about 

 the celestial sphere somewhat like the torrid zone on the earth's sur- 

 face, we shall leave two spherical caps whose united area will exactly 

 equal that of the belt just one hemisphere. From Argelander's 

 gauges it may be calculated that the number of stars inside these 30 

 circles is to that outside nearly as 2 to 1, for stars of the ninth magni- 

 tude, and about as 2 to 1 for the eighth, diminishing with brighter 

 stars. This condensation increases without interruption, to the Milky 

 Way itself. The law holds also with stars visible to the naked eye, 

 though not so conspicuously ; for these, Mr. Peirce found the same 

 ratio to be only as 4 to 3. He was also surprised to see that the stars 

 were very little more numerous in the track of the Milky Way than 

 at a distance of 20 from it, the decrease in density appearing almost 

 suddenly about 30. But as we approach the sun, the rate of conden- 

 sation becomes greater again. Of the twenty stars classed as first mag- 

 nitude by the best observers, fifteen are within the 30 circles ; and of 

 the five outside, but two, Arcturus and one far southern star, are equal 

 in brightness to the average of the twenty. We have no right, however, 

 unless we are dealing generally with a very great number of stars, to 

 take light as a reliable indication of distance. Of our twelve nearest 

 neighbors yet recognized, being all that have a parallax greater than 

 one sixth of a second, and distant from us less than twenty years' 

 journey of light, four are telescopic stars, to which attention was at- 

 tracted by their large proper motion. Ten stars out of these twelve, 

 it should therefore be added, are either in the Milky Way or within 

 15 of it. The exceptions are two minute stars in Ursa Major. 



Will these facts enable us to decide what is the actual form of the 

 immense cluster of stars in which our sun holds so humble a rank ? 

 We may conclude from them, with safety, that the strongly marked 

 and surprising concentration of brightest and nearest stars in the ga- 

 lactic plane is irreconcilable with a generally prevailing uniform dis- 

 tribution, and agrees hardly better with Struve's theory of condensa- 

 tion in parallel planes. For this theory, it will be seen, requires a 

 more decided concentration with a greater distance, the planes of equal 

 density appearing to approach the galactic circle and each other as do 

 the parallel lines of a perspective drawing. We do see some tendency 

 of this kind in telescopic magnitudes, so that we might suppose that 

 Struve's theory began to express the facts at the distance of the faint- 

 est visible stars unless it could be shown that the density of aggrega- 

 tion in the central plane also varies at different distances. In Mr. 

 Peirce's opinion, photometric observations have proved that this den- 

 sity increases from the seventh to the ninth magnitude, and that there- 



