4 



Hans Henie 



As can be seen, the arrangement is so symmetrical and the time of exposure so 

 constant that the Harvard Map forms a most homogeneous material which cannot 

 be otherwise than well suited for a discussion of the apparent distribution of the stars. 



2 The Star Density. 



One copy of the Harvard Map is in the possession of the observatory of 

 Lund, Sweden. This copy was placed at my disposal for statistical examination. 



The first thing to do was to examine the star density on the plates. 



The star density on a photographic plate I define as the munber of stars per 

 square centimeter. 



The density in one point accordingly depends on the real star density of the 

 corresponding point of the sky, of the angular value of one centimeter at the part 

 of the plate in question, and of the time of exposure and the distance from the 

 centre of the plate. These questions will be discussed in the following. 



3. The Determination of the Star Density. 



In order to get the number of stars per square centimeter a most simple 

 method is applied. The plates are negatives and consequently the images of the 

 stars are black points on a transparent ground. The plates are therefore placed on 

 a paper divided into squares of one mihi meter, with thick lines for every centimeter. 



The density may by this means be determined in any part of the negative. 



Two rectangular axes were drawn on the paper, and the plate was placed, so 

 that the approximative centre of the photograph coincided with the origin, and the 

 outlines parallel to the axes. 



As the number of stars according to circular 71 in a total is about 1,5 Mil- 

 Hons I refrained from counting them all and choose the scheme given in fig 1. 

 The centinieter-lines are here drawn. The outside thick lines are the contour of 

 the plate, the interior the outlines of the exposed part. In the spuares marked 

 with a cross all the stars have been counted. As will be seen the scheme is sym- 

 metric to the centre. In this way I get a total of one hundred counts for every 

 plate, and as the area of the plates is not quite 400 square centimeters a little more 

 than of all the stars will be counted, or ca 0,4 Millions. 



The counts are all. made in good day-light under the same conditions through 

 a lens magnifying about 3 times. 



As the density is not as a rule great the counts are easily made, the milli- 

 meter lines giving an excellent assistance. 



As regards the images these latter are generally very fine in a considerable 

 large part of the centre of the negative, even those of the fainthest stars being 

 visible. Towards the margins the images of the brighter stars are distorted and 

 those of the fainther ones difficult to discover. 



