GREAT SUN SPOTS. 



303 



outer corona.' He said it was nothing of the kind ; 

 yet he looked and saw the outer corona just as the 

 other had drawn it ; but he had overlooked that it was 

 the inner corona he was drawing, until his attention 

 was called to it in that way. 



On the same occasion Mr. Stone pointed out 

 another defect of ordinary vision, as an instrument of 

 scientific research, which is well worth noticing. He 

 said very truly, that as soon as any feature has arrested 

 the attention, it becomes prominent ; another person 

 may not catch the same feature, and, passing it over, 

 seizes upon some other point and brings it out more 

 strongly. Photography has no weakness of this kind, 

 at least where due care is taken to use the same kind 

 of plates and instruments, nearly equal in size and 

 similar in quality, when comparison is to be made 

 between pictures taken by different observers or at 

 different stations. 



Knowledge, June 23, 1882. 



GREAT SUN SPOTS. 



WHATEVER success science may have, or fail to have, 

 in predicting terrestrial weather, there can be no 

 doubt astronomers have learnt to predict with con- 

 siderable correctness the occurrence of the mighty 

 solar storms which produce what are called sun spots. 

 They cannot yet say that on such and such a day, or 



