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♦ KNOWLEDGE ♦ 



[May 5, 1882. 



May IG ; l)ut probably most of our readers are more 

 familiar witli half-past eight than with half-past twenty). 



Thus ill lons-itiido 31° 37' E., lotitiiclo 26° 32' N., a poiut close upon 

 the Nile, the duration of the total jihaae is Im. 12s., and the middle 

 at 20h. 31m. 28s. locrvl moan time. The central line crosses the 



Xile about a degree north of Luxor, one of the stations occupied for 

 the observation of the last transit of Venus. 



The eclipses in the map represent the outline of the 

 moon's shadow (the umbra or total shadow), at the suc- 

 cessive epochs mentioned in the above table. Some 

 readers may, perhaps, be interested to learn how the 

 shape and position of the shadow (its size being deter- 

 mined by the calculated duration) have been deduced 

 from a simple process of construction, which also gives 

 other useful information. 



Draw the semicircle SZN, to represent the sky at 

 Station 3 (where most of the observers win be) at the 

 moment of central eclipse, N being north point, S the 

 south, the east and west points at O, and Z the zenith, 

 or point vertically overhead, so that OZ is perpendicular 



