I've often heard that medieval glass windows are thicker at the bottom because glass flows like a fluid.
我经常听说中世纪的玻璃窗底部更厚，因为玻璃像液体一样流动。
2
I've often heard that medieval glass windows are thicker at the bottom because glass "flows" like a fluid.
我经常听说中世纪的玻璃窗底部更厚，因为玻璃像液体一样“流动”。
3
If the glass were kept hot enough, it would flow over the molten tin until the top surface was also flat, horizontal and perfectly parallel to the bottom surface.