CENSUS OF THE SKY SAMPSON. 189 



limiting brightness of stars recorded varies upon each plate with the 

 purit}^ of sky and the elevation above the horizon. I will only allude 

 to this difficulty and say that a scale was determined and w^as applied 

 to each plate in a way that is practically beyond criticism. Standard 

 specimens of the results were photographed within the eyepiece of 

 the measuring microscope for comparison with the plates and were 

 used for the estimation of tl-we magnitudes of all the stars. The count- 

 ing then proceeded. Two computei"s were employed on the work and 

 it occupied them for two years. Success depended yerj much on 

 skill. After the counting had proceeded for a few weeks one of the 

 earlier plates was recounted and the number of stars detected was in- 

 creased by 50 per cent. The whole of these early plates were there- 

 fore repeated and, fortunately for finality, subsequent practice did 

 not increase the numbers any more. Only the magnitudes from the 

 twelfth to the seventeenth were counted, as the maternal was already 

 available for stars brighter than the twelfth. These were found 

 partly in some counts made at Harvard of stars from magnitude 2 to 

 4.5, partly in some counts of Schwarzschild for magnitude 5 to 7.5, but 

 chiefly from the Greenwich Astrographic Catalogue from magnitude 

 9 to 12.5, and a special Greenwich photometry with the Franklin- 

 Adams 6-inch lens for magnitude 6.5 to 9.0. The standard bases of 

 all these, I need hardly say, were most carefully brought into adjust- 

 ment. The results of this laborious work are contained in a table. 

 (A diagram representing the table Avas shown on the screen.) Bm is 

 the number of stars of magnitude m and brighter in each zone; its 

 logarithm is charted here in place of the number in order to make the 

 diagram more compact. In this diagram is contained the net out- 

 come of the counts, the distribution of stars, zone by zone, for every 

 magnitude. 



All the eight curves, representing the eight zones, are independent, 

 and their similarity, which strikes us at once, is convincing proof 

 of their reliability. The}^ tell us that in every zone the proportion 

 of stars of the various magnitudes is the same, as far as the eye can 

 follow. If we look closely into the numbere it appears that there 

 is perceptible a slight gradual increase of the proportion of the 

 fainter stars as the galaxy is approached. Beyond this there is a 

 gradual increase in density in the whole number of stars in the zones, 

 so that at the equator of the galaxy it is three times as dense as at the 

 poles. The progress is quite gradual over the whole sky. The 

 galaxy does not produce a sudden rise in the numbers, and simply 

 drops into the statistical register of the whole. Statistically, in spite 

 of the striking contrasts you have seen, the " divine disorder " of the 

 heavens, there are no other features than this, a gradual condensation 

 amounting at the limit to threefold toward the galaxy accompanied 



