234- Notices respecting New Books. 



was found to include 84 gauges containing 6258 stars, giving an 

 average of 74 - 50 stars to a field. The average would have been 

 much higher if, instead of following the course of this circle, a zone 

 of equal breadth pursuing the irregular line of maximum intensity of 

 the Milky Way had been chosen, which in some places deviates by 

 several degrees from the great circle which expresses its general 

 situation. Judging from the course of the counted gauges only, the 

 mean density of stars in the medial line of the actual galaxy in that 

 part I have observed would be somewhere about 90 stars to the field, 

 but this must be considered as exclusive of the more densely clus- 

 tering masses." — P. 380. 



On the northern side of the galactic circle the average number of 

 stars to a field was found to be as follows : — In the zone extending 

 from 0° to 15°, 51'28 ; from 15° to 30°, 23'47 ; from 30° to 45°, 

 14*46 ; from 45° to 60°, 7*71. The number of gauges taken in those 

 zones were respectively 321, 195, 68 and 21. 



" Nothing," says Sir John Herschel, " can be more striking than 

 the gradual but rapid increase of density on either side of the Milky 

 Way as we approach its course, and the reproduction of nearly the 

 same law of graduation on the north side which holds good on the 

 south, so far as the comparative paucity of the gauges taken in that 

 direction allow us to judge. On the whole, this induction, founded 

 as it is on the actual enumeration of 68948 stars contained in 2299 

 fields, must be admitted as decisive of the specific point in question, 

 and as completing the evidence to the same effect afforded by Sir 

 William Herschel's observations in the northern hemisphere." 



Calculating upon the above averages the number of stars visible 

 enough to be distinctly counted in the 20-foot reflector over the whole 

 sphere, it will be found to be 5,331,572, or somewhat less than five 

 and a half millions. " That the actual number is much greater there 

 can be little doubt, when we consider that large tracts of the Milky 

 Way exist so crowded as to defy counting the gauges, not by reason 

 of the smallness of the stars, but their number." 



It will be understood that great local departures from the law of 

 distribution above indicated occur in all regions, and nowhere more 

 remarkably than in the Milky Way itself, whose irregularities of 

 breadth and structure are most conspicuous and singular ; but with 

 the exception of portions of the galaxy, nothing was found in any 

 part of the heavens meriting in the smallest degree to be regarded 

 as systematic, as respects those deviations from perfect regularity. 

 So purely local are they, that on a careful revision of the whole chart 

 Sir John found it difficult to specify any considerable areas over 

 which an average density of stars prevails materially differing from 

 what might be expected from the law above indicated, regarded as a 

 function of the galactic polar distance. 



Another interesting question remains, namely, whether the in- 

 creased frequency of stars in approaching the Milky Way is observable 

 in respect of stars of all classes of magnitude indifferently. In order 

 to ascertain this point, not only the total numbers of stars were set 

 down in counting the gauges, but those of all the several magnitudes 



