when I took precisely the same quantity and quality of materials which had been reduced to a uniform powder, as fine as flour, by grinding the mixed materials under edge stones, my glass, instead of requiring ten or twelve hours for fusion, became beautifully fluid in four and a-half to five hours. When I first tried this fine ground material in my furnace, I patiently watched the whole process hour after hour; the inert mass of dry white powder lay quietly under the rushing current of flame passing over it, without showing any symptom of fusion. At last I sought relief for my over-fatigued eyes by half an hour's turn up and down the yard; and on my return into the glass-house, I was astonished to hear a curious sound issuing from the furnace, closely resembling the noise given out by a frying-pan when cooking fish; on the application of my eye to the peep-hole of the furnace, I saw that the level of the glass had risen an inch or two, and that a rapid boiling was going on, caused by the disengagement of gas resulting from the rapid reaction of soda on the silicic acid. I scarcely need say how greatly I was pleased at witnessing in a first experiment so important a result, and so distinct an example of the value of a little of this so-called "dangerous knowledge."

Up to this period the fusion of glass in large crucibles was universal, and the reverberatory furnace which I had erected at Baxter House for this purpose was the first in which glass was made on an open hearth, and the parent of all those bottle furnaces in which the fusion of glass is carried on in open tanks. It was here also that the hollow box roof was first used in reverberatory furnaces -- a form of roof afterwards employed by me so economically in the reverberatory melting furnaces used in the early days of the Bessemer steel manufacture. The immense economy, in time, consumption of fuel, and cost of large melting-pots, resulting from the fusion of glass on the open hearth of a reverberatory furnace was accompanied by one great disadvantage, viz ., the tendency of molten matter to fall from the roof of the furnace into the bath, and thus spoil the glass. It was found that whenever the underside of the furnace roof was exposed to an excessively high temperature, the alkaline vapours from the bath beneath caused a fusion of the brickwork, and tears, with their long tails, would fall slowly from above and discolour the glass in the bath beneath. It was mainly to counteract this injurious action that I invented the thin box roof which entirely cured this defect, while the durability of the furnace arch was at least four to one as compared to the ordinary solid form. How well I still remember the trouble and anxiety these tears from the roof caused me, and how I watched through the eye-holes of the furnace the effects of the alkaline vapours on the hollow box roof when it was first under trial. I looked ceaselessly into the fierce glare of the furnace, with but a piece of thick glass between my eye and the bright molten mass, only eighteen or twenty inches distant. When watching by the hour at a time to see if a single tear was formed on the roof, the eye accommodated itself to the intense light, and all within that glorious mass of incandescent matter could be seen in its minutest details. I remember one peculiar circumstance that stood out from all the rest; while one of the hollow firebricks of the roof was in a condition of plastic clay, the brickmaker had taken hold of it, and a hollow caused by his thumb was beautifully delineated on the underside of this particular brick; it happened to be opposite the eye-hole, and was an excellent mark whereby any change in the state of the roof could, from time to time, be observed. This must have been as far back as 1847, but that thumb-mark is as indelibly impressed on my memory as it was on the plastic clay. How many hours in succession I have watched that mark through the fierce heat and blinding light of the incandescent furnace I cannot now take upon myself to say, but my whole heart and mind were so absorbed in the investigation that I never gave a thought to the fearful risk I ran of destroying my sight. Now, when I recall these facts vividly to memory, I can realise the folly I was guilty of, and can, in all humility, thank Heaven that I am not at this moment a blind old man.

It is now just forty-nine years since I succeeded in fusing the materials used in the manufacture of glass on the open hearth of a reverberatory furnace, in about one-third the time and with one-third the fuel required for its fusion in the large and expensive glass pots then in use. But there was still one great desideratum: the glass fused in pots was usually blown into long round-ended cylinders or muffs, the ends of which had to be opened while the glass was still hot and plastic -- an operation requiring great skill and dexterity on the part of the glass-blower. These open-ended cylinders, when cold, were slit from end to end by a diamond, and again heated until sufficiently soft to be spread out flat on the smooth stone bed of a furnace specially constructed for that purpose; after which they had to be ground and polished, if made into what is known as patent plate.