Navigators calculated the water depth by identifying the point where the rope exited the water and counting the markers. The piece of lead tied to the end of the rope was often indented on the bottom and the indentation filled with tallow or fat. Small fragments of the bottom such as clay, sand, gravel, etc. By examining sea bottom samples, navigators could often determine where they were. Would you consider taking a trip of several thousands of miles without a map?
Cabot did that. Even in the world he knew, charts were unavailable. Printing presses were not known, so maps were individually drawn. Map makers were unable to relate correctly the relative position of distant geographic features.
Instead, directions to get from place to place took the form of written instructions, called rutters. The ancient mariners did not sail in warm, dry wheelhouses feet above the water, but on the open deck just a few feet above, and sometimes, in the waves.
They became acutely aware of their surroundings. Land birds foretold of land nearby; swarms of fish and kelp identified shallows. The usual direction of winds and cloud types were all part of their intuition.
Navigation in John Cabot's time was very coarse by today's standards. But his awareness of his surroundings, his prudence,and his courage allowed him to traverse the Atlantic and explore the island of Newfoundland and its rugged shoreline. A 16th Century Brass Astrolabe. A Cross-Staff. Plate XVII. In David W. Taylor between pages 56 and A Nocturnal from H. The Sapphire was a 32 gun, 5th rate, frigate that was in Newfoundland to protect the English migratory fishery. Indeed, some examples could probably be considered to be works of art in their own right.
The functionality of the astrolabe was also extended, to the point where it could be used for literally hundreds of different purposes. Many fine examples of astrolabes were produced in the Islamic world during a period stretching from the ninth to the thirteenth centuries CE.
Islamic explorers used the instrument to study the heavens for the purposes of navigation, whilst Islamic scholars made similar observations in order to determine prayer times, and to find the direction in which Mecca lay.
Much of the scientific knowledge of the Islamic world eventually found its way to Europe via Spain, and a number of notable examples of astrolabes were produced in Europe during the Renaissance period. The quadrant is an instrument for measuring both the altitude of celestial objects and the angular distance between them.
It is similar in in its basic functionality to the astrolabe, although somewhat less sophisticated and simpler in construction. It is believed to have first appeared around CE following a design proposed by Claudius Ptolemy circa 90 - circa CE , an Egyptian-born Greek mathematician and astronomer among other things.
Ptolemy lived in Alexandria, and was a citizen of the Roman Empire. The quadrant is as its name suggests in the shape of a quarter-circle, and can be used to measure angles up to ninety degrees. In larger versions of the instrument, a moveable arm called a radius is attached to the apex of the quadrant, and is used to measure angles.
Artwork showing 17th century astronomers using a large quadrant. The illustration above is an early 18th century copperplate engraving on paper attributed to Philipp Florinus von Pfalz-Sulzbach , and shows astronomers at work.
One of them is using a large quadrant, probably to measure the angles between various stars and planets. Like the astrolabe, the quadrant has been used for many different purposes, and many different types of quadrant have been created. Early versions of the so-called mural quadrant were created by drawing the outline of the quadrant on a suitable wall. Later versions were created by constructing a wooden or metal framework, which was then attached to a wall.
Other large quadrants were housed in their own frame. The frame-based quadrant shown below is one of the artifacts that can be seen in the pretelescopic Beijing Ancient Observatory in China, and was constructed in Mural and frame-based instruments were typically used to measure the altitude of, and angular distances between, celestial objects. In gunnery, the quadrant was often used to measure the angle of elevation of the barrel of a cannon or other form of artillery.
Quadrants of various types could also be used to determine the time. Other types of quadrant were used for surveying and navigation. The mariner's quadrant shown below also known as a geometric quadrant is part of a collection of nautical instruments housed at the National Maritime Museum, Greenwich, London, and dates from around Note the sights at the top and bottom end of the right-hand edge of the quadrant, which form a simple alidade an alidade is a device that allows an observer to determine the line of site between themselves and some distant object.
As you can see, a plumb bob is suspended from a pin affixed to the apex of the quadrant. In order to measure the altitude of some celestial object such as a star, the observer must hold the quadrant upright i. The idea is that you should be able to see the star or whatever object you are interested in finding the altitude of through both sights of the alidade.
The plumb bob is allowed to hang down vertically, and the point at which it crosses the limb is read to give the angle of elevation. It could be quite difficult to maintain the instrument in the correct position and check the position of the plumb bob at the same time. Often, one person established a line of sight using the quadrant, while a second person recorded the position of the plumb bob.
The accuracy of the instrument was limited by its size smaller instruments tended to be less accurate than their larger counterparts. Accuracy was also rather dependent on the conditions in which the instrument was being used. High winds and heavy seas, for example, would have made accurate observations almost impossible.
The cross-staff is a navigational instrument, an early form of which is thought to have been invented in around BCE in Chaldea an ancient land bordering the upper end of the Persian Gulf , although its use for navigation does not appear to have occurred until the fourteenth century CE. The main component is a long wooden rod or staff, usually about thirty-six inches long, having a square cross-section and a graduated scale marked along its length on each of the four sides.
The other components consist of much shorter vanes cross-pieces that are designed to slide back and forth along the length of the main staff. Each vane of which there are usually four in number is unique in terms of both its length and how it is graduated. When the cross-staff is in use, only one vane is used at a time, each being intended for use with the markings on a different side of the main staff. The website features a number of reproductions created by him, together with some very useful background information.
The cross-staff gets its name from its cruciform appearance it may also be occasionally referred to as a Jacob's staff or Jacob staff , although this name is also sometimes used to refer to other types of apparatus, so we will stick with the name cross-staff. The cross-staff as we know it today was first described the Jewish mathematician Levi ben Gerson of Provence, France , although its invention is credited by some sources to Jewish astronomer and physician Jacob ben Makir ibn Tibbon who also lived in Provence during the same period.
The instrument has been variously used for astronomical observations, for surveying, and for navigation. It can be used to measure the angular height of an object relative to the user, or to measure the angular distance between two objects in the night sky.
The use of the cross-staff for navigation is believed to have first been suggested in by the German mathematician Johannes Werner It was typically used to measure the elevation of the Sun at mid-day in order to find the current latitude of the observer. Each vane or cross-piece is used to measure a different range of angles. The user holds one end of the cross-staff close to one cheek in order to sight along its length, and slides the vane along the main staff until its lower edge lines up with the horizon and its upper edge lines up with the Sun.
The vane is then held in place and lowered so that its position in relation to the markings on the main staff can be read. The reading gives the altitude usually in degrees of the Sun above the horizon. A cross-staff in use image credit: Canadian Museum of History. In some ways, the cross-staff was ideal for use at sea as a navigational instrument.
It was light, portable and relatively simple to make. On the other hand, it did suffer from some limitations. The instrument relied on the ability of the observer to accurately line up two different points simultaneously.
However, the human eye is not actually capable of focusing on two different points at the same time, which meant that there was always the possibility of errors being made, particularly if the user was inexperienced. The further the angle falls outside this range, the greater the likelihood of error. There was also the small matter of having to look directly into the Sun whilst measuring its altitude - never a particularly good idea, although the use of smoked glass provided a partial solution.
The problem of having to look directly into the sun was eventually solved by the introduction of an instrument called the back-staff. This instrument measured the altitude of the Sun by allowing it to cast the shadow of a vane called the shadow vane onto another vane the horizon vane mounted at the front of the instrument. The user stood with their back to the Sun, and sighted the horizon through slits in the sighting vane mounted at the rear of the instrument and the horizon vane.
The shadow vane would be moved along the forward arc until its shadow fell on the horizon vane, and its position on the arc then recorded. Easier to use than the cross-staff although according to some sources less accurate , the back-staff gradually became more widely used.
Eventually, both instruments would be superseded by the octant. An 18th century back-staff image credit: National Museum of American History. The back-staff illustrated above is typical of those that had evolved by the mid-seventeenth century from the instrument originally designed by English navigator and explorer Captain John Davis in The version designed by Davis, which became known as the Davis Quadrant , was a significant improvement on existing versions of the back-staff.
It also overcame some of the shortcomings of other navigational instruments in use at the time, including the cross-staff, astrolabe and quadrant. The theodolite is an instrument used in surveying for measuring angles in both the horizontal and vertical planes. Its invention, in around , is accredited to the English mathematician and surveyor Leonard Digges of Kent , although arguably its origins can be traced back considerably further.
The Greeks used an instrument called a dioptra for measuring the position of stars in the night sky. This instrument was later adapted by the Romans for the purpose of measuring angles during surveying, and in this more evolved form had started to resemble its sixteenth century counterpart. Digges called his instrument a theodelitus , and it consisted of a divided circle and square with a compass in the centre, as illustrated below.
Although equipped with a sighting device, it was missing the telescopic tube found in more modern versions.
This position which does not change the equilibrium conditions, makes very convenient the use of this balance. The barometer. The simplest barometer is the Torricelli's tube who filled with dry mercury in order to not contain neither gas, nor vapor above mercury. The pressure measured by the barometer is expressed in millimeter of mercury. It makes it possible to meausure altitudes indirectly. The mercury contained in the tube rises of 1 mm by 10 m rise.
It is very useful for wheather forecasting. The students had to identify and locate the ancient instruments described in this page in the museum. Do you know ancient instruments? Click on Download the questionnaire. Here is the list of the ancient instruments decribed in this page The astrolabe The armillary sphere The octant The sextant The gregorian telescope The compass The roman balance The hour glass The compass The Roberval's balance The barometer.
The astrolabe The astrolabe exists since Antiquity before J. The armillary sphere The armillary sphere, invented by Hipparque consist of five circles of metal. These varouis circles represent : the ecliptic the meridian line the equator the positions of stars the fifth mobile circle carries two sights at the end of an diameter to carry aimings. In its center, a small sphere represents the Earth. The Octant This apparatus belogs to the same family as the sextant.
The gregorian telescope In the telescope of gregory a real , reversed image is formed in the principal focus of the large mirror placed at the bottom of the tube. The compass A piece of magnetized iron is aligned spontaneoulsly in the North-South axis. The manufacturers of instruments of navy were unable to solve the three problems raised by the compass : The magnetic north is not the true north The difficult conditions disturb the compass The iron and the steel of the hull of the ships causes disturbances It is only about that we solve these problems.
Many scholars credit Hipparchus, an ancient Greek astronomer and mathematician, with the invention of the astrolabe. By measuring the distance of the sun and stars above the horizon, the astrolabe helped determine latitude, an important tool in navigation. Another tool, the magnetic compass, which had been invented in the twelfth century, was improved upon during the Renaissance. Early wooden astrolabes were invented in Ancient Greece. Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design, adding circles indicating azimuths on the horizon.
In the Middle Ages, metal astrolabes were created. The Earth has an iron core that is part liquid and part solid crystal, due to gravitational pressure. Because astrolabes measure things that move in the sky, they have both fixed and moving parts. The main difference between Sextant and Astrolabe is that the Sextant is a angle measurement instrument and Astrolabe is a astronomical instrument.
A sextant is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Read More. Table of Contents. What are the principles of occupational health and safety?
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