One of the earliest of these direct processes proposed to allow the molten glass to flow out from the furnace, downward, through a narrow slit formed in the side or bottom of the tank. The impossibility of keeping such a narrow orifice open and at the same time regulating the flow of glass made this proposal impracticable, although the use of drawing orifices has been revived in one of the latest processes. The American process, which is said to be at work under commercial conditions, is not entirely satisfactory in this respect--that it is a mechanical process for the production of cylinders and not of flat sheets, so that the subsidiary processes of splitting and flattening still remain to be carried out as before. In this process an iron ring is lowered into the bath of molten glass through an aperture from above; the glass is allowed to adhere to the ring which is then slowly raised by mechanical means, drawing a cylinder of glass with it. If left to itself, such a cylinder, owing to the effects of surface tension in the glass, would soon contract and break off, but the American invention avoids this action by chilling each bit of the cylinder as soon as it is formed. This is done by the aid of air blasts delivered upon both sides of the glass as it emerges from the bath, and it is claimed that by this means cylinders of any desired length and diameter may be drawn direct from the bath. The obviously great mechanical difficulties connected with these operations have probably been overcome, but not without sacrificing much of the simplicity of the arrangement, and the relative economy of this process as a whole, compared with the hand process, has yet to assert itself.