Woman: In our lab today, we’ll be testing the hypothesis that babies can count as early as five months of age. The six babies here are all less than six months old. You’ll be watching them on closed-circuit TV and measuring their responses.

The experiment is based on the well-established observation that babies stare longer if they don’t see what they expect to see. First, we’re going to let two dolls move slowly in front of the babies. The babies will see the two dolls disappear behind a screen. Your job is to record, in seconds, how long the babies stare at the dolls when the screen is removed.

In the next stage, two dolls will again move in front of the babies and disappear. But then a third doll will follow. When the screen is removed, the babies will only see two dolls. If we’re right, the babies will now stare longer because they expect three dolls but only see two.

It seems remarkable to think that such young children can count. My own research has convinced me that they have this ability from birth. But whether they do or not, perhaps we should raise another question – should we take advantage of this ability by teaching children mathematics at such a young age? They have great untapped potential, but is it good for parents to pressure young children?
39. Narrator: What is the experiment designed to demonstrate?
40. Narrator: Which of the babies’ reactions would be significant for the purposes of the experiment?
41. Narrator: How does the professor explain the babies’ behavior?
42. Narrator: What implication of her research is the professor concerned about?

Man: I’m glad you brought up the question of our investigations into the makeup of Earth’s interior. In fact – since this is the topic of your reading assignment for next time – let me spend these last few minutes of class talking about it. There were several important discoveries that helped geologists develop a more accurate picture of Earth’s interior.

The first key discovery had to do with seismic waves – remember they are the vibrations caused by earthquakes. Well, scientists found that they traveled thousands of miles through Earth’s interior. This finding enabled geologists to study the inner parts of the Earth. You see, these studies revealed that these vibrations were of two types: compression – or P – waves and shear or S waves. And researchers found that P waves travel through both liquids and solids, while S waves travel only through solid matter.

In 1906 a British geologist discovered that P waves slowed down at a certain depth but kept traveling deeper. On the other hand, S waves either disappeared or were reflected back, so he concluded that the depth marked the boundary between a solid mantle and a liquid core. Three years later another boundary was discovered – that between the mantle and Earth’s crust.

There’s still a lot to be learned about Earth. For instance, geologists know that the core is hot. Evidence of this is the molten lava that flows out of volcanoes. But we’re still not sure what the source of the heat is.
43. Narrator: What is the purpose of the talk?
44. Narrator: What important discovery about seismic waves does the instructor mention?
45. Narrator: What did the study of seismic vibrations help geologists learn more about?
46. Narrator: What did P and S waves help scientists discover about the layers of Earth?

Woman: You may remember that a few weeks ago we discussed the question of what photography is. Is it art, or is it a method of reproducing images? Do photographs belong in museums or just in our homes? Today I want to talk about a person who tried to make his professional life an answer to such questions.

Alfred Stieglitz went from the United States to Germany to study engineering. While he was there, he became interested in photography and began to experiment with his camera. He took pictures under conditions that most photographers considered too difficult – he took them at night, in the rain, and of people and objects reflected in windows. When he returned to the United States, he continued these revolutionary efforts. Stieglitz was the first person to photograph skyscrapers, clouds, and views from an airplane.

What Stieglitz was trying to do in these photographs was what he tried to do throughout his life: make photography an art. He felt that photography could be just as good a form of self-expression as painting or drawing. For Stieglitz, his camera was his brush. While many photographers of the late 1800s and early 1900s thought of their work as a reproduction of identical images, Stieglitz saw his as a creative art form. He understood the power of the camera to capture the moment. In fact, he never retouched his prints or made copies of them. If he were in this classroom today, I’m sure he’d say, “Well, painters don’t normally make extra copies of their paintings, do they?”

47. Narrator: What is the professor mainly discussing?
48. Narrator: What question had the professor raised in a previous class?
49. Narrator: What does the professor imply about the photographs Stieglitz took at night?
50. Narrator: Why did Stieglitz choose to not make copies of the photographs?