MILKY-WAY KECENTLY TAKEN AT SYDNEY OBSERVATORY. 109 



18^ inches in diameter. Tn the experiments in photographing 

 the Milky- Way at Lick Observatory, it was estimated by Mr. 

 Barnard that on one of their plates measuring 10x8 (mine are 

 6x8) there were 64,000 stars ; if we may compare the plates it 

 would appear that in the same area I have about 160,000 stars 

 where Mr. Barnard has 64,000, which indicates that the stars are 

 more numerous in the part of the sky about Alpha Centauri than 

 in the northern part of the Milky- Way. I feel sure that so far 

 we have not had a single photo taken under the best conditions, 

 that is a clear bright night with little wind, and when we do 

 get such weather I shall not be surprised if the regions now 

 photographed yield 50 or 100 per cent, more stars, for such hazy 

 bad weather as we have had for months past is most unfavourable 

 for this work. 



I have brought one photograph of the region in which the 

 Southern Cross is situated to show you what the coal sack is like. 

 You will see that there are hundreds of stars strewn over it, and 

 a curious zig-zag line of stars extends from Alpha Crucis to the 

 solitary 7th magnitude star in the coal sack, and that there are 

 two small and striking clusters of stars, but this picture was taken 

 on a very bad night and does not show as many stars here as it 

 ought to. It will be observed that a ring of stars incloses the 

 dark space, but it is more remarkable for the greater brightness 

 of the stars than for their numbers. The photograph of the 

 region round Eta Argus shews a condensation of stars as close, 

 or nearly so as that round Alpha Centauri, and is perhaps still 

 more striking owing to the numbers of clusters of comparatively 

 bright stars on it, and I think that the curious grouping, curved 

 and straight lines, circles, ellipses, etc., which may be traced here 

 are more remarkable than in the other plate. You will observe that 

 there are two negatives of this region, one taken with the longer 

 dimensions of the plate in It. A., the other one with it in declina- 

 tion, but the point to which I wish to call your attention is that 

 the better one of the two was exposed for two hours and forty 

 minutes and the other one for three hours and five minutes. The 

 difference between them is striking. The longer exposure was on 

 a fine night, but it had a slight and almost invisible haze to contend 

 with, and this apparently slight drawback was sufficient to reduce 

 the number of stars it contains by fully one-half, although it had 

 a longer exposure by fully twenty-five minutes. The positive from 

 the better of these two plates is most successful ; the photographer 

 has caught just that exposure and density of the image giving 

 the best and most pleasing picture conditions, which are not easy 

 to attain. In this case it serves to bring out with great clearness 

 the marvellous beauty of this portion of the heavens. I will not 

 try to picture it for you in words because the task is a hopeless 



