Get value of Label set using jQuery on Server Side in ASP.Net using C# and VB.Net

hello sir, 

          i ma trying to store longitude and latitude vallue in label control but it gets null on ppostback..

          how to store it in database then?

  $.ajax({
                        type: "POST",
                        url: "MerchantRegistration.aspx/SaveLocation",
                        data: JSON.stringify(location),
                        contentType: "application/json; charset=utf-8",
                        dataType: "json",
                        success: function (data) {
                            //  alert(data.d[0]);
                            $('.longitude').html(data.d[0]);
                            return true;
                        }
                    });

in webmethod:

[System.Web.Services.WebMethod]
    public static string[] SaveLocation(string lattitude, string longitude)
    {
        //   "Latitude: " + lattitude + " Longitude: " + longitude;
        string[] a = new string[2];
        a[0] = longitude;
        a[1] = lattitude;
        HttpContext.Current.Session["longitude"] = longitude;
        HttpContext.Current.Session["latitude"] = lattitude;
        return a;

    }
on server click:

 protected void OnTest(object sender, EventArgs e)
    {
       string str = lblLongitude.Text;
    }

reply asap.

thank you.