THE STELLAR UNIVERSE. 



from the galactic pole, very slowly at first, but with great rapidity 

 when the galactic latitude was much diminished. 



72. An analysis of the observations of Sir "W. Herschel, in the 

 northern hemisphere, was made by Professor Struve, with the 

 view of determining the mean density of the stars in successive 

 zones of galactic latitude ; and a like analysis has been made of 

 the observations of Sir J. Herschel, in the southern hemisphere. 



If we imagine the celestial sphere resolved into a succession of 

 zones, each measuring 15 in breadth, and bounded by parallels 

 to the galactic circle, the average number of stars included within. 

 a circle, whose diameter is 15', and whose magnitude, therefore, 

 would be about the fourth part of that of the disc of the sun or 

 moon, will be that which is given in the second column of the 

 following Table. 



Average number 



It appears, therefore, that the variation of the density of the 

 visible stars in proceeding from the galactic plane, either north or 

 south, is subject almost exactly to the same law of decrease, the 

 density, however, at each latitude being somewhat greater in the 

 southern than in the northern hemisphere. 



73. The regions of the heavens, which extend to a certain 

 distance on one side and the other of the galactic plane, are 

 generally so densely covered with small stars, as to present to the 

 naked eye the appearance, not of stars crowded together, but of 

 whitish nebulous light. This appearance extends over a vast 

 extent of the celestial sphere, deviating in some places from the 

 exact direction of the galactic circle, bifurcating and diverging 

 into two branches at a certain point which afterwards reunite, and 

 at other places throwing out off-shoots. This appearance was 

 denominated the Via Lactea, or the galaxy,* by the ancients, 

 and it has retained that name. 



The course of the milky way may be so much more easily and clearly 



* From the Greek word y&\a t yaXaxros, "milk." 

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