The AstrolabeĪnother ancient instrument used for navigation is called the astrolabe. Most steamboat folks wouldn’t bother with such flowery language and just said “by two” or some such variation. In fact, the likely familiar, if apocryphal, saying “by the mark, twain” is a steamboat term that meant the depth of a river was exactly two fathoms, or twelve feet, deep. Lead lines, and their more modern cousin the log line, are still useful for rivers and waterways that experience unpredictable or seasonal changes to their depth.Ī more contemporary example of this is the Mississippi River. This was especially useful because the Nile experienced seasonal floods, so the depth of the river changed periodically. Military vessels still use this type of compass, especially submarines.Ī hollow lead weight on a length of rope may not seem like much of a tool, but ancient sailors would lower the line and determine the depths of the water they were in.Ī ball of animal fat in the weight would also bring up material on the ocean floor, allowing them to determine their location from the dirt or sand they brought up.Īncient Egyptians used these lead lines to measure the depth of their water route, usually the Nile. Occasionally, it is checked against a GPS to make sure it is still accurate. The spinning nature of the gyroscopic compass meant that it always pointed to true north, and even bad seas would not affect it.Since the magnetic compass was not completely accurate (pointing to the Earth’s magnetic north pole instead of its true north on a map) it evolved into the gyroscopic compass, used today.Over the course of the centuries, the compass changed from being encased in an air bubble (a dry compass) to a bubble of water (a liquid compass) to a magnetic compass.This was the type of compass that seemed to make its way through Chinese and Arab traders into Europe. The compass changed from a lodestone ladle to an iron needle rubbed with a lodestone then placed in a bowl of water.Interestingly, these early compasses (made in the shape of a ladle or spoon on a bronze plate decorated with the cardinal directions) pointed towards the Earth’s Southern Pole, instead of those today which point to the North Pole.
If the lodestone was allowed to spin freely, it would spin to align with the Earth’s magnetic field. The compass was usually a piece of lodestone or magnetite, a type of iron ore with magnetic qualities.
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