opengl es - culling lines on the back of a globe

I am drawing a simple outline of the world using GL_LINE_STRIPs (in WebGL).

I want to not draw those lines that are on the other side of the spinning globe.

Using Nicol Bolas approach below I am trying to determine if a point is going away from the camera or not:

scene.map = {
    vbo: gl.createBuffer(),

    draw: function(pMatrix,mvMatrix,camera,t) {
        gl.useProgram(this.program);
        gl.uniformMatrix4fv(this.program.pMatrix,false,pMatrix);
        var spin = mat4_rotation(t,[0,1,0]);
        mvMatrix = mat4_multiply(mvMatrix,spin);
        gl.uniformMatrix4fv(this.program.mvMatrix,false,mvMatrix);
        var nMatrix = mat4_inverse(mat4_transpose(mvMatrix));
        gl.uniformMatrix4fv(this.program.nMatrix,false,nMatrix);
        gl.uniform3fv(this.program.camera,camera);
        gl.uniform4fv(this.program.colour,[0,1,0,1]);

        gl.enableVertexAttribArray(this.program.vertex);
        gl.bindBuffer(gl.ARRAY_BUFFER,this.vbo);
        gl.vertexAttribPointer(this.program.vertex,3,gl.FLOAT,false,3*4,0);
        var ofs = 0, parts = this.data.ofs;
        for(var part=0; part            var start = ofs;
            ofs += parts[part];
            gl.drawArrays(gl.LINE_STRIP,start,ofs-start);
        }
        gl.disableVertexAttribArray(this.program.vertex);

        gl.bindBuffer(gl.ARRAY_BUFFER,null);
        gl.useProgram(null);
    },
    program: createProgram("precision mediump float;\n"+
            "attribute vec3 vertex;\n"+
            "uniform mat4 pMatrix, mvMatrix, nMatrix;\n"+
            "varying vec3 n;\n"+
            "void main() {\n"+
            "   gl_Position = pMatrix * mvMatrix * vec4(vertex,1.0);\n"+
            "   n = (nMatrix * vec4(vertex,1.0)).xyz;\n"+

            "}\n",
            "precision mediump float;\n"+
            "uniform vec4 colour;\n"+
            "uniform vec3 camera;\n"+
            "varying vec3 n;\n"+
            "void main() {\n"+
            "   if(dot(camera,n) < 0.0) discard;\n"+
            "   gl_FragColor = colour;\n"+
            "}\n",
            ["pMatrix","mvMatrix","colour","camera","nMatrix"],

            ["vertex"]),
    data: getFile("json","data/world.json"),
};
var pts = [], deg2rad = Math.PI/180;
for(var i=0; i    var lng = scene.map.data.pts[i] * deg2rad,
        lat = scene.map.data.pts[i+1] * deg2rad;
    pts.push(-Math.cos(lat)*Math.cos(lng),Math.sin(lat),Math.cos(lat)*Math.sin(lng));
}
pts.push(0,0,0); // centre of sphere, for sprite z-culling trick

gl.bindBuffer(gl.ARRAY_BUFFER,scene.map.vbo);
gl.bufferData(gl.ARRAY_BUFFER,new Float32Array(pts),gl.STATIC_DRAW);
gl.bindBuffer(gl.ARRAY_BUFFER,null);

and to draw it:

var pMatrix = createPerspective(60,canvas.width/canvas.height,0.1,4),
    eye = [-2,0,0],
    mvMatrix = createLookAt(eye,[0,0,0],[0,1,0]);
scene.map.draw(pMatrix,mvMatrix,eye,t); 

However, this is only drawing the left hemisphere rather than the front:

How can I correctly compute the normal of a point, and the position of the camera?