AR. 
90. W. A. Norton on Comets. 
. 2 2- k s 
Reducing, € aS =1-———“z 
pr cos a 
: ‘ : : PY One 
Transposing coordinates to point X, we have, <= Tan ee 
ee ok eae . 
and z= ising” >. Substituting and reducing, 
Lanning REY ee a OF). 2= A eo tae oo (8) 
pr k sina 
- This is the equation of 2, 
a parabola; the diameter 
through X makes an an- Vv 
gle 6 with XR (fig. 2) de- 
termined by the equation 
cot f= + or by laying 
off LP=2X, and joining N 
Pwith X. The parameter 
of this diameter=X.cot a 
n 
sin ?. 
To find the focus and 
vertex lay off on the di- 
ameter produced the dis- 
tance XY = ee -cos?6, draw YK perpendicular to the 
diameter; the vertex will be on this line. Through the point 
n where this line crosses the tangent XZ, draw nm perpendic 
le X7 and with ~ widen eee describe a circle 
around X as a centre; the point F in which this circle er 
is the focus. Drawing FK parallel to XP, we have ihe ee 
the vertex. The parameter of the axis = Xcotasin®.sin*P= — 
h , 
ae its effect while the particle is in its vicinity, and 
nee from it, where the change of direction and the differ 
Z and NX has Pecit considerable, it 1§ 
edingly small in comparison with the sun’s action. shat 
the accuracy of our results, let us investigate the distance ™" 
