formed using dip furnace 21 and lifting device 32 constructed as described above will be explained next first the end of metal rod 1 is inserted into guide tube 28 at the bottom of dip furnace 21 until its top end projects a little way above dip furnace 21 and is gripped by chuck 33 next glass 29 in granular form is supplied to the space a between electrodes 24 and 25 heated to 300 u00b0 600 u00b0 c and thereby melted by a gas burner or the like electrodes 24 and 25 are then connected to constant current power source 30 when glass 29 melts electric current i begins to flow between electrodes 24 and 25 through glass 29 when the current begins to flow heating by the gas burner is stopped once the current has started to flow the glass which is in the flow path of the current is subjected to the thermal energy of this current so that it continues to melt despite the fact that heating by the gas burner has been stopped and as it does so the current i continues to increase the space a in dip furnace 21 is formed such that electrodes 24 and 25 approach each other more closely in proportion to the height of the upper surface of the glass liquid base 23 is cooled by means of water cooling pipes 27 and since the glass in the vicinity of base.