The Evolution of the Sciences 



through a small hole drilled through one of its 

 sides and suitably widened on the inside, throwing 

 an image of the sun on to the opposite side of the 

 camera; when a small lead disc, slightly larger 

 than the pencil of light, was interposed between 

 the image of the sun and the hole, its shadow 

 covered the image and appeared surrounded 

 by a graduated ring of weak light. This was 

 naturally looked on as an image of what occurs 

 in the case of an eclipse; the assumption that 

 the irregularities of the lunar disc allow more 

 light to pass where they are sunken and less 

 where they project, accounted for the irregu- 

 larities of the corona and for the glories radia- 

 ting around it. 



This hypothesis of diffraction is not more 

 acceptable than that of a lunar atmosphere ; the 

 phenomena adduced by Delille actually exist, but 

 their laws, which to-day are perfectly well known, 

 could not in any way account for the corona or 

 for the protuberances. However, the eighteenth 

 century was satisfied with the two explana- 

 tions we have mentioned. Science had not, at 

 that time, acquired the habit of rigorous criticism 



which, during the past century, has ensured its 



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