1. OK, now, um, a sort of paradigmatic art form of the Middle Age was stain-glass art, stain glass, of course is simply glass that has been colored and cut into pieces and re-assembled to form a picture or decorative design, to truly experience the beauty of this decorative glass, you should see it with light passing through it, especially sun light, which is why stained-glass is usually used for windows.
2. But, of course, it has other uses especially nowadays, anyway, the art of making stain-glass windows developed in Europe, um, during the middle Ages, and was closely related to church buildings. In the early 1100s, a church building method was developed that reduced the stress on the walls, so more space could be used for window openings, allowing for large and quite elaborate window designs.
3. Well, led is strong and flexible so it’s ideal for joining pieces of glass cut in different shapes and sizes, but up to the 15th century, the lead strips also helped created the design, they were worked into the window as part of the composition, they were used to outline figures to show boundaries, just like you might use solid line in a pencil drawing.
4. Yes, with really large windows it took more than one piece of glass, so you still needed led strips to hold the pieces together, but the painters actually tried to hide them, so it was different from before when the lead strips were part of the design and it’s different because with painted-glass the idea of light coming through to create the magical effect wasn’t the focus anymore.
5.A: Professor, since we are going to talk about changes in animal populations in the wild, I'd like to ask about something I read in an article online, about how the population size of some animal species can affect other animal species, and how other environmental factors come into play too.
B: Right. Relationships between animal species in a given ecosystem can get pretty complex, because in addition to predator-prey relationships, there are other variables that affect population size.