1. 39904/2 WHAT IS CLAIMED IS: l'.J A process of manufacturing sheet glass by supplying molten glass to a drawing eone and drawing glass from that cone as a continuous ribbon which is guided through zones In which die glass sets and cools* characterised In that In at least one aone along the ribbon path where the viscosity of the glass is not less than 7*6 13 to ^ poises and not more than 10 poises > <κ*4 a gas-displacing force is exerted periodically at first in a direction across die ribbon path and then in the opposite direction thereby to cause a luctuating displacement of gases across the ribbon*) 2. A process according to Claim 1» characterised in that a said gas-displacing force Is periodically exerted in at least one zone along die ribbon path where the viscosity of the glass is not less than 1010 poises·' 3·< A process according to any preceding claim* wherein the ribbon of glass is cooled while passing upwardly through a vertical annealing shaft the cross-section of which is locally Reduced at the bottom tA define an , entry slot fo the ribbon* characterised in that a said gas-displacing force is periodically exerted in said entry slot. A process according to any preceding claim, wherein the ribbon of glass is cooled while passing upwardly through a vertical annealing shaft the cross-section of which is locally reduced at the bottom to define an entry slot for the ribbon, characterised in that a said gas-displacing force is periodically exerted in at least one zone in said vertical shaft. 5· A process according to claim 1 or 2, wherein the ribbon of glass is bent over a bending roller preparatory to being advanced through a horizontal annealing shaft, characterised in that a said gas-displacing force is periodically exerted in at least one zone which is downstream of the said bending roller along the ribbon path. 6. A process according to any preceding claim, characterised in that said fluctuating displacement of gases is brought about substantially without increasing the rate of cooling of the glass ribbon. 7· A process according to any preceding claim, characterised in that there is at least one said zone along the ribbon path where displacement of gases across the ribbon path occurs and where such displacement is exclusively caused by the periodic exertion of gas-displacing force in at least one direction. 8· A process according to any preceding claim, characterised in that in at least one said zone along . the ribbon path a said gas-displacing force is periodically exerted in one direction and in a reverse direction across the ribbon path, the forces acting in said different directions across the ribbon path being alternately exerted and relaxed out-of-phase thereby to cause displacement of gases on one or each side of the ribbon first in one direction across the ribbon and then in a reverse direction across the ribbon. 9· A process according to claim 8, characterised in that in at least one said zone along the ribbon path a said gas-displacing force is periodically exerted in one direction and in a reverse direction across the ribbon path, the forces acting in said different directions being exerted at positions which are substantially directly opposed across such path and being alternately exerted and relaxed out-of-phase. 10. A process according to claim 8 or 9>. characterised in that in at least one said zone along the ribbon path a said gas-displacing force is periodically exerted in one direction and in a reverse direction across the ribbon path, each exertion of force in said one direction immediately following or coinciding with the relaxation of force in said reverse direction. 11. A process according to any preceding claim, characterised in that there is at least one said zone along the ribbon path where displacement of gases across the ribbon path occurs, due to successive exertions of -61+- force in that zone at a frequency such that a steady state of the gas currents along the ribbon path does not become established or does not become established for sufficiently long a period for the glass to be adversely affected thereby. 12· A process according to any of claims 8 to 10, characterised in that there is at least one said zone along the ribbon path where such an out-of-"phase exertion and relaxation of gas-displacing forces occurs and where the frequency of exertion of force in each direction is such that the period of each cycle from the commencement of one exertion to the commencement of the next exertion of force in that direction is not more than 10 minutes. 13· A process according to claim 12, characterised in that the force exertion period and the relaxation period constituting each said cycle are in a ratio of from 1:2 to 2:1. 11+· A process according to claim 12 or 13* characterised in that each force exertion period of each said cycle is from 1 to 10 seconds. 15· A process according to claim 11+, characterised in that the force exertion period and the relaxation period of each said cycle are of substantially equal duration. l6. A process according to any preceding claim, characterised in that in at least one said zone along the ribbon path a said gas-displacing force is periodically exerted at only one side Of the ribbon. 17· A process according to any preceding claim, characterised in that in at least one said zone along the ribbon path, a said gas-displacing force is periodically exerted on each side of the ribbon. 18. A process according to any preceding claim, characterised in that in at least one said zone along the ribbon path, a said gas-displacing force is periodically exerted by blowing gas into the environ-ment of the ribbon. 19· A process according to claim 18, characterised in that in at least one said zone along the ribbon path, a said gas-displacing force is periodically exerted by blowing gas into the environment of the ribbon at a speed of from 1 - 50 m/scc. 20· A process according to claim 18 or 19, characterised in that in at least one said zone along the ribbon path, a said gas-displacing force is periodically exerted by blowing gas into the environ-ment of the ribbon under a pressure in the range lOOg - lOOOg/cm . 21· A process according to any preceding claim, characterised in that in at least one said zone along the ribbon path, a said gas-displacing force is periodically exerted by the action of mechanical means in the environment of the ribbon. 22· A process according to any preceding claim, characterised in that gas-displacing forces causing displacements of gases in at least one direction across the ribbon on one or each side thereof are also exerted in at least one zone along the ribbon path where 7.6 the viscosity of the glass is less than 10 poises. 23· A process according to claim 22, characterised in that gas-displacing forces causing displacements of gases in at least one direction across the ribbon on one or each side thereof are exerted in a lower portion of the zone through which the glass ribbon is drawn and in which it becomes dimensionally set. 2-4·· A process according to any preceding claim, characterised in that molten glass flows into said ribbon from the full depth of a quantity of molten glass in a channel into which molten glass is continuously fed. 25· A process according to any of claims 1 to 23, characterised in that molten glass flows into Said ribbon from the upper levels of a mass of molten glass in a channel into which molten glass is continuously fed. 26. A process according to any of claims 1 to 23, characterised in that said ribbon of glass is drawn from molten glass floating on a mass of material of higher specific gravity. 27. Apparatus for use in manufacturing sheet glass, comprising a drawing chamber and a contiguous annealing s aft, and means for drawing a continuous ribbon of glass into such drawing chamber from a drawing zone fed with molten glass and conducting the ribbon along a path extending through such drawing chamber and annealing shaft, characterised in that the apparatus comprises means for periodically exerting a gas-displacing force in at least one zone along, the ribbon path where the viscosity' of the glass when the 7 ό apparatus is in use is not less than 10 * poises and not more than 10"^ poises, -and in—at le-a-&fr—erte— direction^across the ribbon path, thereby to cause a fluctuating ; displacement of gases across the ribbon. 28. Apparatus according to claim 27, wherein the said annealing shaft is a vertical" shaft the cross-section of which is locally reduced at the bottom to define an entry slot for the ribbon, characterised in that means is provided for periodically exerting a said gas-displacing force in said entry slot. 29. Apparatus according to claim 27 or 28, wherein the said annealing shaft is a vertical shaft the cross-section of which is locally reduced at the bottom to define an entry slot for the ribbon, characterised in that means is provided for periodically exerting a said gas-displacing force in at least one zone in said vertical shaft. 30o Apparatus according to claim 27, wherein there is a bending roller about which, when the apparatus is in use, the glass ribbon is bent preparatory to being advanced through said annealing shaft, which shaft is substantially horizontal, characterised in that means is provided for periodically exerting a said gas-displacing force in at least one zone which is downstream of the said bending roller along the ribbon path. 31· Apparatus according to any of claims 27 to 30, ' characterised in that means is provided for periodically exerting a said gas-^displacing force in one direction and in a reverse direction across the ribbon path, in at least one said zone along such path, and in that there is timing means, for causing said forces acting in said different directions across the ribbon path to be exerted and relaxed out-o -phase thereby to cause displacement of gases first in one direction across the ribbon and then in a reverse direction across the ribbon. 32· Apparatus according to claim 31 , characterised in that there is means for exerting said out-of-phase force at positions which are substantially directly opposed across the ribbon path. 33· Apparatus according to claim 31 or 32, characterised in that means is provided for periodically exerting a said gas-displacing force in one direction and in a reverse direction across the ribbon path, in at least one said zone, and in that there is timing means for causing each exertion of force in said one direction immediately to follow or to coincide with the relaxation of force exerted in said reverse direction., k Apparatus according to any of claims 27 to 33, characterised in that means is provided for periodically exerting a said gas-displacing force in at least one direction and at one side only of the ribbon in at least one said zone along the ribbon path* 35· Apparatus according to any of claims 27 to 3 , characterised in that means is provided for periodically exerting a said gas-displacing force in at least one direction on each side of the ribbon, in at least one said zone along the ribbon path. 36. Apparatus according to claim 35, characterised in that means is provided for periodically . exerting a said gas-displacing force in at least one said zone on each side of the ribbon and in the vicinity of one margin thereof, and there is timing means for causing the forces on opposite sides of the ribbon to be exerted alternately*. 37· Apparatus according to any of claims 27 to 36, characterised in that means is provided for causing a said gas-displacing force to be periodically exerted in at least one said zone in the vicinity of one margin of the ribbon and in one direction across the ribbon, and also to be periodically exerted in the vicinity of the opposite margin of the ribbon and in a reverse direction across the ritTbon, on the same side thereof, and there is timing means for causing said forces acting in opposite directions across the ribbon path to be exerted alternately. 38. Apparatus according to any of claims 27 to 37, characterised in that there is means for periodically exerting gas-displacing forces in at least one said zone, in the vicinity of each of the opposed margins of the ribbon and on eaoh side thereof , to cause gas displacements across the ribbon, and there is timing means for causing gas-displacing forces to be exerted at the said places according to a predetermined cycle to cause displacements of gas first in one direction and then in a reverse direction across the ribbon on each side thereof. 39. Apparatus according to claim 8 , characterised in that there is said timing means which operates to cause the gas-displacing forces acting in one direction across the ribbon on opposite sides thereof, in a given zone along the ribbon path, to be exerted simultaneously and alternately with the forces acting in the reverse direction across the ribbon in that zone. kO. Apparatus according to claim 38, characterised in that there is said timing means which operates to cause the forces acting in one direction across the ribbon on one side thereof to be exerted simultaneously with forces acting in the opposite direction across the other side of the ribbon and in alternation with forces which reverse the gas displacement at each side of the ribbon. l» Apparatus according to any of claims 27 to O, characterised in that there is means for periodically exerting a said gas-displacing force in at least one said sone along the ribbon path by blowing gas into the environment of the ribbon, 2. Apparatus according to claim ■ i+1 , characterised in that in at least one said zone along the ribbon path there is at least one gas ejector and means is provided for periodically exerting a said gas-displacing force by blowing gas into the environment of the ribbon through such ejectoro 1+3· Apparatus according to claim 1+2, characterised in that in at least one said zone along the ribbon path there are gas ejector devices for exerting gas-displacing forces at different positions in the environ-ment of the ribbon, a common supply line for such devices, and gas-distributing means comprising electrically controlled pneumatic valves for sequentially connecting different ejector devices to said common line. 2+2+· Apparatus according to any of claims 27 to 2+3, characterised in that there are apertures in the peripheral wall of the annealing shaft and controllable closure means for controlling flo.v of guses through suc apertur cj under the action of natural draught "O ihat gas-displacing forces are periodically exerted n at least one direction across the ribbon by such flow of fics., , 5" A paratuc according to any of claims 27 to 1+1+, characterised in that in a least one said zone along the rib on path, there is at least one propeller for periodically exerting a said gas-d :· s lacing force. l|.6o Apparatus a- ;cor ing to c.ny of elains 27 to 1+5, character sed in that r»1ear..i is alio provided for exerting gas-displacing, forces across th ribbon path or. one oi' each side ereo in u- lowe portion of the c av/irj chEtirib r ' ppo.rr.tve seconding to any o: ~l?,^s 27 to ij.6, characterised in that It comprise 3 a Γ..Ό .Ι ten ^lasp feed channel for holding a bath of moltcri ijlass of such depth that molten ss flo ;:: into ^he vVf on fro:.a the full depiih of fjuc hat ., l+80 Apparatus according to any of claims 27 to 1+6, characterised in that it comprises a molten glass feed channel for holding a bath of molten glass of such depth that the molten glass which flows into the ribbon is derived from the upper levels of such bath. l>.9c Apparatus according to any of claims 27 to 1+6, characterised in that it comprises a molten glass feed channel along which molten glass feeds to said drawing zone while floating on a mass of material of higher specific gravity. 50. A process of manufacturing sheet glass, • substantially as herein described with reference to the accompanying drawings 51» Sheet glass when manufactured by a process according to any of claims 1 to 26 and 50. 52« Apparatus for use in manufacturing sheet glass, substantially as herein described with reference to the accompanying drawings. P. O. Box 33116 , Tel- Avi Attorneys for Applicant -71+-