How explorers used mathematics to help them navigate.
Chip log
The chip log was a quarter circle of wood attached to a line that had been knotted at intervals of approximately 14 metres. The quarter circle was thrown over the side of the ship, and a sailor would then count how many knots went over the side in a given time. From this, the captain could estimate how fast the ship was travelling. Today, the speed of a ship is still expressed using the unit of measurement of knots.
Marine astrolabe
The marine astrolabe was a heavier version of an astrolabe. It had holes cut out of it to stop it blowing in the wind. It had a rotating pointer to measure the altitude of the Sun or a star. The captain would move the pointer until the Sun's light shone through holes at both ends, or the star could be seen. Then, they would read off the angle of the pointer from a scale along the edge of the astrolabe. The angle could then be looked up in the astronomical tables that many ships carried. This told the captain the latitude that the ship was travelling at. Unfortunately, the measurements would often be quite inaccurate.
Could you imagine holding up a heavy brass astrolabe on the rolling deck of a ship in the middle of a storm?
Could you imagine holding up a heavy brass astrolabe on the rolling deck of a ship in the middle of a storm?
The quadrant
The quadrant was a quarter circle of wood or brass, marked along its curved edge with a 90 degree scale. A plumb bob hung down from the centre of the instrument. The top edge was lined up with a star, and its angle above the horizon was measured from where the bob crossed the scale.
Like the astrolabe, it was used to estimate a ships latitude.
Like the astrolabe, it was used to estimate a ships latitude.
The compass
Originally invented by the Chinese in the 11th Century, the compass uses a magnetised needle, that swings to indicate the direction of magnetic north. The Chinese discovered that if you repeatedly stroked a needle with a compass, and then placed it on the surface of a glass of water, that it always rotated to the direction of north. Why don't you try making one yourself?
The compass pictured on the left is known as a 'dry compass'. It was invented by German navigators in the 13th Century. Why do you think it was important for sailors to able to use a 'dry compass'?
The compass pictured on the left is known as a 'dry compass'. It was invented by German navigators in the 13th Century. Why do you think it was important for sailors to able to use a 'dry compass'?
Ship's clock
The other vital piece of navigational equipment was the ship's clock. These had to be wound up by hand to keep accurate time. Often, they weren't that accurate anyway, but they were good enough for a skilled captain to record how far a ship had sailed. When combined with the compass, and the chip log, the captain could track how far a ship had sailed in any direction. This was the only way that a captain had to estimate the longitude of the ship. If any of the three measurements (time, speed, or direction) were wrong, the captain could misjudge how far the ship had travelled in an easterly or westerly direction.
Investigating the mathematics of sundials.
Now you know all about the importance of the stars and the sun to early navigators, try completing the investigation into sundials by following this link.