EI. A. P. Barnard on the Zodiacal Light. A01 
or ought never to be present at all, may be ascertained by the 
equation 
co-lat.—obliquity of ecliptic=g’, 
for the first ; and by the equation 
co-lat.+ obliquity of ecliptic=¢’, 
for the second. Putting D=9000, as in the March number of 
this Journal, o’=26°; and the equations foregoing will give the 
latitude 40° 32’ as the limit of perpetual apparition of the light, 
and 87° 28’ as that of its perpetual occultation. 
By assuming, in the triangle ZSQ, 6=18°, and the position of 
on the circle H’R’, we shall find that the visibility of the 
light as an arch of which the extremity is beneath the horizon 
when the sun is 18° depressed, will be limited to places between 
the latitudes at which the maximum inclination of the ecliptie to 
the horizon is not less than 26° on the one hand, and the mini- 
mum not greater than 28° 34’ on the other; and the season of 
its greatest conspicuousness at any given hour, or at any given 
depression of the sun, may be found by putting I1=28° 34’ in 
the equation given in the note on p. 231 of the last number of 
the Journal,* viz. 
cos I=sin L cos O—cos L sin O sin A, 
University of Mississippi, Oxford, March 15, 1856. 
> Jicase the maximum inclination of ecliptic to the horizon is not so great as 
28° 84’, substitute that maximum itself for 
Srconp Szrres, Vol. XXI, No. 63, May, 1856. 51 
