What Had to Exist First

Why then and not earlier · Page 1 of 2

Name Date
DIRECTIONS: Why did each of these arrive when it did, not centuries before? Fill in the table.
Each one was waiting for something else to exist.
The thingArrivedWhat it was waiting forAvailable sinceThe gap
1. The printing press1440paper1150
2. The telescope1608ground glass lenses, in spectacles1290
3. The light bulb in houses1880a way to make electricity1800
4. The wheeled suitcase1970the wheel3500 BC
Fill in the last column: subtract.
The dates are approximate and that is not a weakness. Paper does not arrive in Europe on a Tuesday, and historians argue about the first battery by a decade or two. A gap of three hundred years survives being wrong by twenty. When the thing you are claiming is much bigger than the error, rough numbers are enough — and knowing when they are is most of using numbers well.
  1. Rows 1 to 3 waited for a part. Row 4 waited for something else. Say what kind of thing that was, and give one other invention that waited the same way.

What Had to Exist First — The Odd One Out

Why then and not earlier · Page 2 of 2

Row 4 is not like the others. Nothing technical was missing from a suitcase with wheels on it in 1850, or in 1350. Wheels were five thousand years old, suitcases were ordinary, and putting one on the other is not difficult.

What arrived in about 1970 was not a part. It was a situation: airports with long smooth floors, people carrying their own bags a very long way, and enough of them to be worth making a thing for.
  1. Somebody says people before 1970 simply did not think of it. Say what is wrong with that, and what a fairer sentence would be.
  2. Pick any invention not on this sheet. What had to exist before it could be made — and how would you check?