Locating Location
Optical Options
Telescopes were invented in the early 17th century and soon became widely used. Sailors found them useful for looking into the distance to see the far-off coast, other ships or events at sea. By doing this, they could not only find out where they were but also avoid danger.
Telescopes are made of a number of curved glass lenses inside a tube which magnify what the eye can see. A number of telescopes are in the Hull Maritime Museum collection, some of which were used at sea and others which may simply have been fashionable collectables used by high-society gentlemen.
Sighting the Skies
The Earth moves in a known pattern, so we can predict its position in relation to the Sun and stars. A sailor could therefore measure the height (or altitude) of the Sun or a star from the horizon to find out his own latitude (that is how far North or South he was on the Earth).
From the 17th century the quadrant was used for this purpose. A sailor would look through the pinhole sights at the Sun or star and measure its angle on a scale. He then transferred this reading into a latitude measurement.
In the late 18th century octants and sextants became a common means of measuring latitude. The sailor looked through a hole towards a 'horizon' glass which was half covered with a mirror. Through this he could see the horizon. He then moved the 'index' arm until the Sun or star shone into the 'index' mirror and its image was reflected into the horizon glass mirror. When this happened, he read a measurement off a scale to find the altitude. He then used mathematics to change this measurement into latitude.
Octants were popular because they were cheap and reasonably accurate. They were usually wooden and contained a series of mirrors and scales which the sailor used to obtain a reading from which he could calculate latitude. Sextants worked on a similar concept but on a different scale and were usually made of metal.
Later instruments for recording position, some of which in the collection date to the 20th century, have included azimuth mirrors which were used to take bearings.
Once measured, seafarers recorded their position at sea on a chart using various scientific instruments. Hull Maritime Museum holds dividers and parallel rulers which were used for this purpose.
