The Evolution of the Sciences 



fifteenth magnitude. It is possible to count 

 on photographs up to six thousand stars, 

 although their number must be greater, because, 

 in the centre of the cluster, many of the luminous 

 points must be superimposed. 



The stars, in their turn, like the nebulae, 

 present the most varied appearances, revealing 

 the diversity of their structure. To the naked 

 eye some appear white, some yellow, and some 

 reddish, while the colour of others at times 

 seems greenish and at others bluish. In the 

 neighbourhood of the Southern Cross 170 stars 

 are contained in a space equal to one-fortieth 

 of a square degree ; a score of the brightest ones 

 present all the colours of the rainbow, so that 

 this group has been compared to a splendid 

 jewel studded with precious stones of every 

 possible water. 



These differences of coloration, which can 

 be further analysed by the spectroscope, appear 

 to be related to the temperature, one and 

 the same star turning, as it cools, successively 

 blue, white, green, yellow, and then red. This 

 shows us that all parts of the primitive nebula 



have not aged with equal rapidity, and here 



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