Nova projects an old drawing. A man in a long coat plants a tiny willow branch in a big pot.
"Hundreds of years ago, a scientist named Jan van Helmont asked our question," she says.
Rocket squints at the pot. "Did he weigh the soil?" he asks. "I would weigh the soil."
"He did," Raven says, reading from her wrist computer. "And he waited five whole years."
Rocket groans. "Five years? I can barely wait five minutes." Then he grins. "Let's see what he found."
Van Helmont dried 200 pounds of soil and put it in a big pot.
He planted a willow shoot that weighed 5 pounds. He gave it only rainwater for five years.
Then he weighed the tree. It weighed about 169 pounds.
He dried and weighed the soil again. It had lost only about 2 ounces.
| What he measured | At the start | After 5 years |
|---|---|---|
| Willow tree | 5 pounds | About 169 pounds |
| Soil | 200 pounds | 200 pounds, less about 2 ounces |
Van Helmont thought the new wood came from water alone.
Today scientists know the plant used water and also carbon dioxide from the air.
Even a great experiment can lead to a new question. That is how science grows.
The willow started at 5 pounds and ended at about 169 pounds.
That means it gained about 164 pounds.
The soil lost only about 2 ounces. That is far less than one pound.
| Statement | True or false? |
|---|---|
| Van Helmont used 200 pounds of dried soil. | ? |
| The willow grew for five years. | ? |
| The soil lost about 164 pounds. | ? |
| He watered the willow with rainwater. | ? |
| Statement | True or false? |
|---|---|
| The willow weighed 5 pounds at the start. | ? |
| Van Helmont thought the wood came from the soil. | ? |
| A great experiment can lead to new questions. | ? |
You analyzed a real historical experiment. Tomorrow you will catch a plant moving water.