In a small saucepan, combine the sugar, water and corn syrup. Bring to a boil and cook until the candy thermometer reads 116 °C (240 °F). Remove from the heat while whipping the egg whites.
In a bowl, whip the egg whites and cream of tartar with an electric mixer until soft peaks form. Pour the syrup in a stream over egg whites, beating constantly until the meringue has cooled and stiff peaks form.