verbatimtex %&latex \documentclass{article} \usepackage{fourier} \begin{document} etex path axe; axe = (0,-60)--(0,60); beginfig(1); for i:=0 upto 12: yy := 50 - (25 / 3 * i); xx := - sqrt(3600 - yy * yy) - 10; drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0); endfor; fill fullcircle scaled 100 withcolor (1,1,.3); fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1); draw axe; for i:=1 upto 7: yy := 50 - i * 12.5; xx := sqrt(2500 - yy * yy); draw (xx,yy)--(-xx,yy) withpen pencircle scaled .5pt withcolor .6white; endfor; label.urt(btex $N$ etex,(0,50)); label.lrt(btex $S$ etex,(0,-50)); endfig; beginfig(2); for i:=0 upto 12: yy := 50 - (25 / 3 * i); xx := - sqrt(3600 - yy * yy) - 10; drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0); endfor; fill fullcircle scaled 100 withcolor (1,1,.3); fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1); draw axe rotated 23; for i:=1 upto 7: yy := 50 - i * 12.5; xx := sqrt(2500 - yy * yy); draw ((xx,yy)--(-xx,yy)) rotated 23 withpen pencircle scaled .5pt withcolor .6white; endfor; label.urt(btex $N$ etex,(0,50) rotated 23); label.lrt(btex $S$ etex,(0,-50) rotated 23); endfig; beginfig(3); for i:=0 upto 12: yy := 50 - (25 / 3 * i); xx := - sqrt(3600 - yy * yy) - 10; drawarrow (-100,yy)--(xx,yy) withcolor (1,1,0); endfor; fill fullcircle scaled 100 withcolor (1,1,.3); fill (halfcircle--cycle) rotated -90 scaled 100 withcolor (.3,.2,.1); draw axe rotated -23; for i:=1 upto 7: yy := 50 - i * 12.5; xx := sqrt(2500 - yy * yy); draw ((xx,yy)--(-xx,yy)) rotated -23 withpen pencircle scaled .5pt withcolor .6white; endfor; label.urt(btex $N$ etex,(0,50) rotated -23); label.lrt(btex $S$ etex,(0,-50) rotated -23); endfig; end