Skip to the content
Peabody TeachFor teachers and grown-ups

The Clock That Solved the Longitude Puzzle

7th grade nonfiction passage about marine clocks and longitude: 243 words, six questions, an answer key and vocabulary.

7th grade nonfiction marine clocks and longitude 243 words

The Clock That Solved the Longitude Puzzle

For hundreds of years, ships crossing the ocean could easily be lost. Sailors could measure how far north or south they were by checking the height of the sun or the stars. That measurement is called latitude. Finding how far east or west they were, which is longitude, proved much harder.

The answer depends on time. The Earth turns once in a day, so every hour of difference between two places equals fifteen degrees of longitude. If a navigator knew the exact time at the home port and could also tell local noon from the sun, the gap between those two times revealed the distance traveled east or west. The trouble was that the clocks of the age used swinging pendulums, and a pendulum fails on a pitching, rolling ship. Changes in heat and damp air also made early clocks run too fast or too slow.

In 1714, the British government offered a large prize to anyone who could find a practical method. A clockmaker named John Harrison spent decades on the problem. He built several sea clocks with clever parts that were not thrown off by a ship's motion or by changes in temperature. His fourth design looked like a large pocket watch. On a voyage to Jamaica in the early 1760s, it lost only a tiny amount of time.

Over the following years, copies of such timekeepers went to sea. Voyages became safer, because captains could finally fix their position with confidence.

Questions

  1. What is latitude? in the text

  2. How many degrees of longitude equal one hour of time difference? in the text

  3. Why did pendulum clocks fail at sea? in the text

  4. Who spent decades building clocks to solve the problem? in the text

  5. Why did a navigator need to know the time at the home port? think about it

  6. How did good clocks make sea travel safer? think about it

Words to know

latitude
distance north or south on the Earth
longitude
distance east or west on the Earth
pendulum
a weight that swings back and forth to keep time
practical
useful in real life
temperature
how hot or cold something is
Share

One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 214 words · Flesch-Kincaid grade 2.8

For hundreds of years, ships at sea could get lost. Sailors could tell how far north or south they were. They looked at the sun or the stars. That is called latitude. But finding how far east or west they were was much harder. That is called longitude.

The answer depends on time. The Earth turns once a day. So every hour of time between two places is fifteen degrees of longitude. A navigator needed the exact time at his home port. He also had to know local noon from the sun. The gap between the two times showed how far he had gone east or west. But old clocks used swinging pendulums. A pendulum does not work on a ship that pitches and rolls. Heat and damp air also made clocks run too fast or too slow.

In 1714, the British government offered a big prize. A clockmaker named John Harrison worked on the problem for decades. He built sea clocks that a ship's motion and heat did not upset. His fourth clock looked like a big pocket watch. On a trip to Jamaica in the early 1760s, it lost only a tiny bit of time.

Soon more such clocks went to sea. Trips got safer. Captains could now find their place with trust.

▲ This passage · 243 words · Flesch-Kincaid grade 7

For hundreds of years, ships crossing the ocean could easily be lost. Sailors could measure how far north or south they were by checking the height of the sun or the stars. That measurement is called latitude. Finding how far east or west they were, which is longitude, proved much harder.

The answer depends on time. The Earth turns once in a day, so every hour of difference between two places equals fifteen degrees of longitude. If a navigator knew the exact time at the home port and could also tell local noon from the sun, the gap between those two times revealed the distance traveled east or west. The trouble was that the clocks of the age used swinging pendulums, and a pendulum fails on a pitching, rolling ship. Changes in heat and damp air also made early clocks run too fast or too slow.

In 1714, the British government offered a large prize to anyone who could find a practical method. A clockmaker named John Harrison spent decades on the problem. He built several sea clocks with clever parts that were not thrown off by a ship's motion or by changes in temperature. His fourth design looked like a large pocket watch. On a voyage to Jamaica in the early 1760s, it lost only a tiny amount of time.

Over the following years, copies of such timekeepers went to sea. Voyages became safer, because captains could finally fix their position with confidence.

■ Harder · 269 words · Flesch-Kincaid grade 10.2

For hundreds of years, ships crossing the ocean could easily lose their way. Sailors were able to determine how far north or south they had traveled by measuring the height of the sun or the stars above the horizon, a measurement known as latitude. Establishing how far east or west they had gone, which is called longitude, proved to be a far more stubborn challenge.

The solution depends on time. Because the Earth rotates once every day, each hour of difference between two places corresponds to fifteen degrees of longitude. If a navigator knew the exact time at his home port and could also identify local noon from the position of the sun, the gap between those two times revealed the distance he had traveled eastward or westward. Unfortunately, the clocks of that era relied on swinging pendulums, and a pendulum cannot function properly on a pitching, rolling ship. Variations in heat and damp air also caused early clocks to run either too quickly or too slowly.

In 1714, the British government announced a large prize for anyone who could devise a practical method. A clockmaker named John Harrison devoted decades to the problem. He constructed several sea clocks with ingenious parts that were not disturbed by a ship's motion or by changes in temperature. His fourth design resembled an oversized pocket watch, and on a voyage to Jamaica in the early 1760s, it lost only a trivial amount of time.

During the years that followed, copies of such timekeepers went to sea in growing numbers. Voyages became considerably safer, since captains could at last fix their position with confidence.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put latitude, longitude, pendulum, practical and temperature on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "The Clock That Solved the Longitude Puzzle"?

It was written for 7th grade. It has 243 words and works out to a Flesch-Kincaid grade level of about 7.0. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

Nothing you do here is sent to us. No sign-in, no ads.