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ASTRO>JOMY. 



7 



sunrise in March and April, and after sunset in August 

 and September. The zodiacal light cc:: cists of a pyramid 

 of faint liglit, wliose base is somewhere near tlie place of 

 the sun, and whose point is at a distance of perhaps oOf 

 from the sun ; the axis of the pyramid being usually in- 

 chned to the horizon, following nearly the direction of the 

 ecliptic. Although it presents to the eye a considerable 

 body of light, yet the light of any portion of it is so feeble, 

 and the definition of its outline is so imperfect, that it 

 cannot be obsc. ,od w^ith a telescope. The observer. 



therefore, should only attempt to observe it with 



the 



naked eye, when the sky is very clear, and when the sun 

 is so far below the hori?:on that no twilight is visible. He 

 should then endeavour, with the assistance of a chart of 

 the star'!', to define as accurately as possible its boandary 

 with reference to the stars ; remarking especially the place 

 jf the point of the pyramid, the width where it rise- from 

 the hori zon, whether its sides are curved, and in what parts 

 the light is brightest. It will be found that these obser- 

 vations are made most accurately by occasionally turning 

 the eye a little obliquely from the zodiacal light. In 

 registering the observation, in addition to the particulars 



*^ 



to be recorded as prescribed abovOj there should be a 

 statement of the latitude of the ship5 the day, the time at 

 the ship (or the Greenwich tiiue and the longitude of the 

 ship), the state of clearness of the sky, and the state of the 

 M^eather for the day preceding the observation. 



Imp7wement of Nojjtical Astronomy. 



8. So much attention has been given to every detail of 

 Nautical Astronomy, that it is very difficult to fix upon 



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