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 Before the invention of clocks in the Middle Ages, a variety of ingenious methods of marking the passing of the hours had
been devised. The sandglass, which we commonly call an "hour-glass," was probably invented in the Mediterranean region
in the 12th or 13th century A.D.
By the beginning of the 17th century, sandglasses were in common usage for marking the passing of time. Until the end of
the 18th century, the sandglass was made of two separate vials, each drawn into a narrow neck at the point where they were
to be joined. A diaphragm of thin sheet brass, drilled with a small hole at its center, was placed between the two vials. The
vials were then joined together with wax or putty and wrapped securely with canvas or cords or both.
Sandglasses were made to run for various periods of time. However, the glasses used in navigation were generally set to
run for one hour, one-half hour, and one-half minute. The hour and half-hour glasses would have been used to determine
the length of the watches (a watch being a four-hour period of time during which one group of seamen were on duty); the
half-hour glass would have been used to determine the times for recording information on the traverse board; and, the
half-minute glasses would have been used to read out the knots-per-hour at which the ship was traveling.
In A Sea Grammar, Capt. John Smith wrote that a ship's captain or master should provision his ship with a
number of sandglasses of various time lengths because there was great breakage during the course of a voyage.
One of the duties of the cabin boy on a ship was to watch the sandglasses. He had to be ready to turn them over when the last of the sand ran from the top half to the bottom half. At the end of each half-hour he had to ring the ship's bell. When the sailors heard the bell, they knew it was time to check the speed and direction in which the ship was traveling. They used the half-minute glass to check the speed of the ship. The information was then marked with pegs on the traverse board.
Bells during a four-hour watch:
- 1 bell - 30 minutes
- 2 bells - 1 hour
- 3 bells - 1 1/2 hours
- 4 bells - 2 hours
- 5 bells - 2 1/2 hours
- 6 bells - 3 hours
- 7 bells - 3 1/2 hours
- 8 bells - 4 hours
Sources
- Text:
- ©2003 by Duane Cline, author of The Pilgrims and Plymouth Colony: 1620. Used by permission of the author.
Illustration:
- Sandglass, English or Colonial America, c. 1750.
- ©2004 by D. Thomas Treadwell.
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