Milkj iray. 333 



In short, if we see a much gi'eater number of stars in cer- 

 tain directions than in others ; if the regions with thickly 

 placed stars form one of the great circles of the sphere ; if 

 the principal arc is double for an extent of 120^ — it is because 

 we are plunged in a group of excessive extent and compara- 

 tively very thin ; because we occupy very nearly the centre of it; 

 and because a second group of the same form meets the first 

 towards the region where our sun, and consequently the earth, 

 are situated. 



If we suppose that the stars of the Milky Way, taking them 

 altogether^ are uniformly distributed throughout all the regions 

 of this nebula ; if we admit, moreover, that the observer gauges 

 this curious portion of the heavens with an instrument, w hose 

 power permits him to reach, in every direction, the last limits of 

 the starry stratum, the number of tars contained in the visual 

 field of the telescope will be, in eacA observation, so intimately 

 connected with the length of the line comprised between the 

 eye of the astronomer and the terminal limit of the stratum, 

 that one of these quantities may always be deduced, by calcu- 

 lation, from the other. Herschel having gauged our nebula, 

 and having estimated, as I have mentioned above, its riches 

 in stars in all directions, was therefore in a condition to de- 

 duce therefrom the corresponding linear dimensions. The 

 table included in his memoir of 1785, gives the distance from 

 the earth to the limits of the Milky Way, that from the earth 

 to Sirius being regarded as unity. 



/ one star, the distance in question is . . 68 



' 10 stars . 127 



20 . . 160 



60 ... . . 218 



When the field -.qq ^ ^ ^ o-rg 



of the telescope \ goo ... . . 347 



includes g^Q '" ^^ . 397 



400 ... . . 4.37 



600 . . 471 



\ 600 . . 500 



W^ithout, therefore, going beyond the limits of direct obser- 

 Tations, the nebula is thus found to be a hundred times more 



