Mathematica Code

wireno = 12; (*The number of wires*)

wires = Table[
   {(i + 0.5)/1.5, (-1)^i},
   {i, -wireno/2, 
    wireno/2 - 
     1}]; (*This table contains the locations of the wires*)

symbcircle[{xi_, yi_}, rad_] = Graphics[{
    White,
    EdgeForm[Thick],
    Disk[{xi, yi}, rad]}];

cdot[{xi_, yi_}, rad_] = Graphics[Disk[{xi, yi}, rad/3]];

ccross[{xi_, yi_}, rad_] = Graphics[{
    Thick,
    {Line[{{xi - rad, yi}, {xi + rad, yi}}],
     Line[{{xi, yi - rad}, {xi, yi + rad}}]}}];

iinsymbol[{xi_, yi_}, rad_] = 
 Show[symbcircle[{xi, yi}, rad], 
  ccross[{xi, yi}, rad]]; (*Symbol for current going into the page*)
ioutsymbol[{xi_, yi_}, rad_] = 
 Show[symbcircle[{xi, yi}, rad], 
  cdot[{xi, yi}, rad]]; (*Symbol for current comng out of the page*)

wiresin[rad_] = Graphics[Show[
   Table[
    iinsymbol[{wires[[n, 1]], wires[[n, 2]]}, rad],
    {n, 1, wireno, 
     2}]]];(*Table containing positions of all "in" current symbols*)
\


wiresout[rad_] = Graphics[Show[
   Table[
    ioutsymbol[{wires[[n, 1]], wires[[n, 2]]}, rad],
    {n, 2, wireno, 
     2}]]];(*Table containing positions of all "out" current symbols*)
\


wiresymbols[rad_] = 
  Show[wiresout[rad], wiresin[rad]]; (*All current symbols*)

r[{xi_, yi_}] = 
  Sqrt[(x - xi)^2 + (y - yi)^2]; (*Distance from {x,y} to {xi, yi}*)

f[{xi_, yi_}] =
  {(y - yi)/r[{xi, yi}]^2,
   -(x - xi)/r[{xi, yi}]^2}; (*Circular vector field*)

ftot = Sum[
   wires[[k, 2]]*f[wires[[k]]],
   {k, 1, 
    wireno}]; (*Sum of effects of all wores (including direction \
governed by y-positon*)

cplot = ContourPlot[
   Sqrt[ftot[[1]]^2 + 
     ftot[[2]]^2], (*Magnitude of resultant vecotr*)
   {x, -6, 6},
   {y, -4, 4},
   PlotPoints -> 50,
   PlotRange -> {0, 6.01},(*We want a line at the top edge, 
   and this ensures it*)
   Contours -> Table[i/3, {i, 0, 18}],
   Frame -> False,
   AspectRatio -> 4/6,
   ImageSize -> 1200,
   ColorFunction -> "Rainbow"];

Show[cplot, wiresymbols[0.07]]