INTRODUCTION. 



XXIII 



XKHULOrS RIXC. AROUND THE SDN. 



We apply to this diagram, as a fair example, the morning observation of September 4, 1854: 

 lat. 22 18' North. Sun rose at 5 h 48 m ; last observation of the morning 4 1 ' 30" 1 ; previous one 

 3 h 30 m . Let E H be the spectator's horizon at 4 h 30 m , and E H 1 at 3" 30 ra . Then E N will 

 equal 158,900,000, and E M 179,100,000 miles*. 



Let ABC represent the boundaries of the Zodiacal Light at 4 h 30", and D E F at 3 h 30 m ; B 

 EOF being the southern boundary, which was permanent; and A G C and D F the northern 

 boundaries, at those respective hours. Now, by referring to the chart for that observation, it 

 will be seen that the opposite sides of the Zodiacal Light, which, at 3 h 30" 1 , at its base, were sepa- 



"- Tin- reader will see that mathematical precision can scarcely be attempted in these numbers ; they are offered only as 

 such careful approximations as the case will admit of ; but these are hcra sufficient. 



