144 



THE APPARENT POSITION OF THE ZODIACAL LIGHT. 



If these results are laid down as points determined by rectangular co-ordinate 



the abscissas representing the variations of absorpt 



xpressed in tenths of a 



magnitude, and the ord 

 the same scale in degret 



the projected points may be 



treme point its course would be doubtful 



curve of some simple theoretical form su 



representing variations in latitude, expressed upon 

 irve passing through the origin and nearly through 



; but beyond the ex- 



drawn with some confidence 



Hence it seemed best to 



ploy 



a 



gested by the graphical result. 



The 



curve selected was a parabola passing through the origin, with its axis parallel 



the 



of abscissas. Upon this assumption, the mean values just obtained for 



iponding variations in absorption and in latitude 



furnish four equations of 



condition, of the form px -f- by 



2 



if 



denote by 2p the parameter of 



■ 



parabola, and by — b the ordinate of the vertex. The solution of these equa- 

 tions by the method of least squares results in the values 2jt? = 4.77 and b 

 1.70. Hence the abscissa of the vertex is — 0.61, and the equation of the para- 

 bola is (y -j- 1.70) 2 = 4.77 (x -4- 0.61), from which values of y in degrees may be 



s parabola was 



obtained for values of 



given in tenths of a magnitude 



Th 



ted, and the 



rected latitud 



d in the two columns of Table II 



next to the last, were mostly found from the chart. 



Results previously reached by other methods for the relation between absorp- 

 tion and latitude did not materially differ from those just given. The method 

 here adopted has the advantage of leaving comparatively little to be arbitrarily 

 determined. 



The experiment was afterwards made of grouping the remainders derived from 

 the inclination of the ecliptic and from the latitude of the axis in Table IV., the 

 form of which resembles that of Table III. 



TABLE IV. 







Evening Observations. 











Morning Observations. 





• 



No. 



Sums. 



Means. 



Av. 



Dev. 



1 No. 

 ] Rem. 



5 



Sums. 



i 



Means. 



Av. 



Dev. 



Hem. 



Incl. 



Lat. 



Incl. 1 Lat. 



Incl. 

 o 



1.5 



Lat. 



Incl. 



Lat. 



Incl. 



3.22 



Lat. 



2.20 



Incl. 



Lat. 



5 



o 



7.5 



o 



0.4 



1.50 



0.08 



0.6 



16.1 



11.0 



o 



2.2 



o 



2.4 



5 



47.3 



1.3 



9.46 



0.26 



2.0 



0.9 



5 



58.0 



2.5 



11.60 



0.50 



2.6 



1.3 



5 



86.4 1 8.7 



17.28 



1.74 



2.3 



0.6 



1 





















• 



4 



212.2 



15.6 



53.05 



3.90 1 



5.1 



0.4 



5 



191.9 



29.9 



38.38 



5.98 



11.1 



3.7 



