© Duane A. Cline 1999
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Navigation: Sandglasses 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 twelfth or thirteenth century A.D. By the beginning of the 17th century sand-glasses 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. Capt. John Smith, in his book entitled A Sea Grammar, states 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. Master Jones of the Mayflower undoubtedly knew the importance of having a number of sandglasses at his disposal on the
ship. A worksheet on sandglasses has been provided in this packet. The teacher might wish to duplicate that page for the pupils
so they can add it to their notebooks. If the page is to be colored by the pupils, you should know that many of the
sandglasses had wooden frames which were simply varnished. Occasionally, however, we find samples of wooden frames
which were painted a deep red. You may wish to have the pupils learn the bell system which would have been used on any ship of this period, and make a
game of testing their memory by ringing bells at appropriate times. If your watch begins at 8 A.M., one bell would be rung
at 8:30; two bells at 9:00; etc. This would have been the correct times for one of the watches on ship. The next watch
would have begun at 12:00 noon (eight bells), with the first bell ringing at 12:30 P.M., etc. 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 lastof 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:
Last modified October 7, 1999
by
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