The Evolution of the Sciences 



These figures may at first sight seem para- 

 doxical, as we know from our experience that 

 opportunities are much more frequent for observ- 

 ing eclipses of the moon than of the sun; but 

 we must not forget that when the moon is 

 eclipsed the phenomenon is visible at all points 

 of a terrestrial hemisphere, whereas, in order to 

 observe a total eclipse of the sun, it is necessary 

 to be within the narrow strip traversed by the 

 moving spot; thus the last total solar eclipse 

 visible in Paris dates as far back as 1724, and 

 the next following one will not occur before 

 2026. 



It would, however, be a mistake to conclude 

 that all total eclipses are equally interesting to 

 science; they may be more or less accessible 

 for observation. Frequently the zone of 

 visibility crosses oceans, regions where the sky 

 is perpetually clouded, or practically inaccessible 

 deserts; and finally the duration of the occulta- 

 tion varies from one eclipse to another, the 

 maximum being eight minutes at the equator 

 and six minutes at the latitude of Paris. Let 



us consider, as an example, one of the latest 



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