At the beginning of the fifteenth century the
technique of navigation differed on almost nothing of use in antiquity,
sailing is almost in sight of the coast using oars or winds of
feature and the pilot was to choose the route through which it had
knowledge of the local defendants, the tides, currents and waterways
the Art of Sailing made possible the removal of the shore without fear
of losing sight of.
The needle, brought from China to Europe by the Arabs and Crusaders,
gave the navigator the opportunity to follow a certain route with no
Lack of instruments to measure time accurately (the stopwatch just appeared in the eighteenth century), the navigator could not measure longitude. Estimated to face the direction and path, nevertheless, the Portuguese navigators ventured up at all stops of the Atlantic, initially with caravels, to double the Cape of Good Hope and the recognition of the winds in the South Atlantic, and , after that, with ships, making exclusive use of cloth round .
The instruments used in navigation were emerging on the need to determine, at sea, the vessel's position. And almost all were adapted from existing instruments and used for other purposes, for the new function. A point common to all is the fact that quite simply measuring angles, between an object and a reference, or between two objects. The big difference between the different tools presented here - quadrant, astrolabe and balestilha - the accuracy, how to use and reference for the measurement of angles. These same instruments were forerunners of more rigorous, using the double reflection, as octante and the sextant, which also used to measure angles.
The use of these instruments for determining latitude where sailing, required the existence of tables where you could see the value of the declination of both the sun and the stars more used. Only the Polar Star, for being near the North Pole land, far from only about 3, 5 - with a declination of 86, 5 - not needed for these tables, but only to have the pilot know the rules of the Polar star .
Quadrante - It was already mentioned and described in many medieval works, particularly in the Libros del Saber de Astronomia, of the thirteenth century. In its primitive form was used, certainly, to measure heights and distances. Adapted to the boat was probably the first instrument of celestial navigation that the Portuguese pilots used. It is Diogo Gomes, navigator of Infante D. Henry, referring to a trip by him carried out, around 1462, that states have "seen the quadrant with the height of the arctic pole. In turn, António de Naiera in its Navigación speculative and Practice, published in Lisbon in 1628, made the following statement on this instrument: "The nautical quadrant, similar to the astrolabe, so he takes to with ease and certainty the height of the sun at noon, with the same ease and certainty with the quadrant will be the height of the stars on the horizon when the night comes to its meridians.
The quadrant was built in wood, taking the form of a quarter of a circle - hence the origin of the name. One of the straight edges were placed the pinnule - also small pieces of wood - with holes, for which "the star stuck. In the vertex of the quadrant was stuck in a hole, a wire-to-bob-length slightly greater than the radius of the instrument. At the free end, was a small weight in metal. The edge was curvilinear with a graduated scale from 0 º to 90 º. To measure the height of the Sun, for example, the pilot had to match the light of this star, through the hole on the upper pinnule, with the hole on the lower pinnule. This was achieved by placing the instrument in the meridian of the star and with a slope very accurately. In that instant, the wire-to-bob indicated the height of the star - angle between the horizon and the star - the zenith distance - angle between the star and the zenith of the observer, depending on just how the instrument is graduated - from 0 º to 90 º or 90 ° to 0 °, the flat edge to edge of the pinnule.
The fact that these instruments are of wood, and possibly one of the reasons why not come to this day any quadrant of the time of discovery.
Nautical Astrolabe - It was, probably, the simplification of the astrolabe planisféric, which was used by cosmography to determine the position of the stars in the sky, the local time from the height of the Sun, or to solve geometric problems. As some of these functions had not much interest for navigation, the nautical astrolabe was only with the option of measuring the height of the stars, because this was the need for use on board ships, by the pilots. If it was originally built in wood, or sheet metal, soon concluded that this did not used to, strictly, be used on board. So is now built in bronze. This gave him the strength and weight appropriate to be used in the sea and minimizing the effects of the balance of the ship. Still, constructed with a body mass, had the disadvantage of providing too much resistance to the wind and make remarks. To remedy this problem, his body was opened, leaving only the two orthogonal diameters. In its center turns a mediclina where two pinnule, with holes, through which, like the quadrant, as' the stick star '. Normally the two upper quadrants astrolabe is engraved a scale of 0 º to 90 º - and this was initially high. Later became a reference zenith. That meant doing one calculation in determining the latitude by the meridian passage of the Sun.
To measure the height observer holding the astrolabe by the ring of suspension - which minimizes the effect of the balance of the vessel in the instrument - and makes a match light the sun, through the hole on the upper pinnule, with the hole on the lower pinnule. If the astrolabe is well constructed, aligned, and with holes of dimensions correct, it is still possible to see the light of the sun, after crossing the two holes, cover the deck.
The use of this instrument by the Portuguese pilots back to the last quarter of the fifteenth century. This is following passage of João de Barros, the description of the first voyage of Vasco da Gama: ... Santa Helena ... which went ashore to make watered and signed to take the height of the sun. Because, as the use of the astrolabe of navigation mister for that there was little time that seafarers take advantage of this kingdom ,...». Many nautical astrolabe come to this day, mostly of Portuguese origin. The largest collection of instruments is held at the Navy Museum in Lisbon.
Balestilha - The first description of
using balestilha appear only in documents of the sixteenth century.
More specifically in the Book of Navy, John of Lisbon (c.1514). In
1529, the fishing vessel was attacked by João Gomes off the coast of
Guinea, by French pirates. Among the things taken by the assailants
had been "needle and astrolabe and balestilha and rules for the art
This instrument is extremely simple and consists of a stick of wood to square - four scales - called viral, about 80 centimeters in length. Over this runs a small piece of wood - of different sizes for each of the scales - called floor. In each of the edges of the viral is a scale according to the size of the floor to use. In a night observing the observer looks at hole in the tip of the viral, to see the star tangential to the upper edge of the floor and the horizon tangent to edge lower. Because the sun can not be targeted directly, when it was intended to measure their height, the observation was made of setback, ie back to the star. In this case, the shadow of the upper edge should be designed in the middle of the floor and sliding both, make it coincide with the skyline. If you look good in its principle of operation is easily concluded that it is identical to that of Kamal, or "the Moor balestilha 'tool found in use in Arab pilots in the Indian Ocean, and discovered on the first voyage of Vasco da Gama. The balestilha was the first instrument of celestial navigation to take as reference the horizon of sea.
Most balestilhas old who came to us and ivory are were built in Holland, between 1596 and 1805.
With all these instruments were made numerous comments, the board of the School-Ship 'Sagres', comparing it with the sextant readings (accuracy of 1 / 10 of a minute). The extensive experience gathered, the balestilha is the most accurate to observe the Sun of setback. The astrolabe gives errors rarely exceed 15 minutes during the day. At night, due to its weight and form to use to 'put the stars', the error increases considerably. In this case the quadrant is easier to use and produces, therefore, better results.
Since the fifteenth century that developments in shipbuilding and the art of sailing ships helped to provide the best of Portuguese requirements for the needs of the time. The sailing needle will have a course of 32 roses instead of 12, the suspension of balance is used since 1537, but since 1560 is known as cardan. D. John de Castro, in 1538, noted by observing the deviation of the needle, 128 years before Dennys and developed a rudimentary method for determining longitude
The first was nonius invented a process for measuring the Portuguese mathematician Pedro Nunes. When applied to a tool, this process allowed the measurements to accurately grade a few minutes, allowing the passage plan with a margin of error of the order of tens of kilometers
The nonius can be described as a pair of graduated scales, usually in millimeters or degrees, which slide over the other. In the second level (which is the nonius itself) can read a portion of the first measurement scale. The nonius is used in caliper and micrometers for precise measurements. In a typical caliper, the main scale is calibrated in millimeters, and provides for measures nonius with accuracy of 0.05 mm.
From the reign of King John II, became the caravels with
artillery guns on deck instead of weapons of little size (falconet,
bombard), which then led. It was also traditional to bring both eyes
painted on the bow season because there the belief that once they see
the way, that tradition continued to this day as evidence in the
existing fishing boats.
Around 1500, the Portuguese invented the "turkish iron" to maneuver the anchors. From 1520 the popas increased from round to square, allowing the guard to open hatch-rudders. Three years later came the flat sides of ships to replace the traditional broken, less resistant. The Portuguese first used the nails of iron in the manufacture of ships and caravels and hence the possibility of making smooth back.
The Portuguese were the first to use nails to preach the taboo of the hull, while northern Europe used wood dowels into overlapping board.
Also the Portuguese gasket was of high quality, the ships of Flanders using a single tow and ill get to Lisbon without having to be tight carenado and again, while the Portuguese pretty good the more than six months of travel to Cochin and Goa, as the Portuguese and Spanish were the first to use lead in the seams of ships and applied, in addition to tow the folder "galagala" consists of lime, tow mixed with oil which gave a bitumen that had lined the inside of the boards of two . A kind of pladur of today. Moreover, the teachers covered the Portuguese side of pitch or tar. To get burned up in pine trees similar to the lime kilns, leaving the resin to drain a tank placed at the bottom of the oven, a gap where the wood was carbonized. The pasty residue obtained after called tar that used to be cooked with vinegar that curdled acquired the name of pitch. The views ranged from what was better, the tar or pitch, but these folders are sealed giving the tone to the black Lusitanian Naus.
The navigation to the tack is, by definition, one that is made with the apparent wind forward to the cross, ie less than 90 ° on the bow of the ship, saying that it is less than 8 quarters. A fourth, therefore, equivalent to 11, 25 or 11 15 '. With the open wind between 90 and 157, 5 (8 to 14 quarters) the ship sails to a wide and with the wind to come by an angle greater than 14 quarters, browse to the stern.
Contrary to an idea more or less general, no sailing vessel can sail against the wind. To move in the direction from which the wind blows - get weather - will have to do edges, browse zigue-zague, a tack greater - smaller angle with the wind - in their sails and equipment permit. As a rule, a vessel of cloth Latin - candles that wear in the machine direction of the vessel (eg carvel) - can come to browse more wind (tack closed) of a vessel of cloth round - candles that wear in the cross direction of the ship (eg ship). The reason is because of the yards - sticks where the scale cloth round - having its forward movement for limited, due to the presence of enxárcias - cables that hold the mast to the edge. As such, the angle at which the sail can receive the wind is always lower than that in which the candle is from the outset to wear bow-stern. This is the basis by which very often poorly explained, it is said that a caravel was walking against the wind. What is not true. It is the sailing for Portugal, from the Mine or the archipelago of Cape Verde, could only be made to tack because the presence of trade winds from northeast (NE) to that required. The vessels were, therefore, differs from much of the coast and to the back off, to make possible the journey, going pass near the Azores. With a caravel, a ship instead of cloth round, the removal, or around the square, would be somewhat lower. But not much. Is that the more fierce is the bowline, the greater the rebate - angle between the bow and direction. In the journey between Cape Verde and the Cape of Good Hope also ships sailed to tack, to a latitude close to the cable. In these circumstances, and most often round ships - ships - to make the trip to India, the remoteness of the western African coast was great and went even close to the Brazilian coast.
Although much has been written about the capabilities of the luff of the Portuguese vessels XV-XVI centuries, the arguments are not always well founded. And not for lack of documentation to mention the limitations of naus and caravels. Indirectly much information is provided by D. António de Ataíde in his work of the Kingdom Travel to India and India to the Kingdom (1608-1612), when referred to bow to the ships sailing and the direction from which the wind blows. More explicit is Father Fernando Oliveira, in his Art of War of the Sea. In general, as a rule practice, based on the documentation available, it appears that a ship could sail round the cloth, the ceiling, with the wind on the 6 quarters - about 68 - from the bow. In turn, a caravel could luff to the wind on the 5 quarters - about 56 - from the bow. However, in any case limits of tack would be to wait about 10 to 15 of rebate on the bow, which made this type of sailing inefficient. It was therefore preferable, there are no obstacles that justify - eg low, islands, cords - opt for a sailing where the wind was less scarce.
Armando Cortesão identified four major milestones in the history of nautical science and cartography: the development of letter-portulano in the thirteenth century, the Mediterranean, the invention of celestial navigation and the consequent introduction of the scale of latitudes in the letters at the end of the fifteenth century; the discovery of the rhumb lines and its representation by a straight line drawn in the letter according to the Mercator projection, and finally improving the stopwatch by Harrisson English at the end of the eighteenth century, which allowed the determination of longitude at sea. Among these steps, the second is almost exclusively Portuguese, while on the Mercator projection can say that she owes much to studies conducted by the great mathematician Pedro Nunes, who discovered the concept of rhumb lines, and whose work would be known to Mercator, who would have been inspired to design the projection that its famous name.
The cartographic representation of the places that were
being discovered by sailors of centuries XV and XVI, was crucial for the
establishment of regular trips to these locations. Only with a more or
less rigorous conditions of navigation can achieve this safely. The
mapping is, among many other factors, a key element to the success of
the Portuguese Discoveries.
If in the fifteenth century the available data on the mapping produced in Portugal are scarce, the situation on the next century is completely different. Are known hundreds of letters, assembled by Avelino Teixeira da Mota and Armando Cortesão in the work Portugaliae Monumenta Cartographica. Is identified most of the authors of these works, although there are some drawings of letters on which it was not possible to discover the identity of the cartographer that done.
As an art mapping in the sense of medieval work of
craftsman, not surprising that the techniques used in the design and
reproduction were transmitted from parents to children. For this reason
we find several families of cartographers as Reinel family, the family
Homem or family Teixeira.
A careful examination of all known copies Portuguese map dated those centuries allows us to see some evidence on the evolution of construction techniques used and the accuracy of the information contained in the letters. The technique of construction was the basis of letters-portulano, characterized by having a "network" of directions radiating from certain points of the letter so that your users can easily know the direction that united two locations represented in any letter. The position of a ship at sea at any moment, can be known if we know which direction in which he sailed and the distance from a previous position. This method is known among historians of the sailing course and with respect. Hence it was essential that the letters had the necessary elements for the sailors could make that direction.
However, with the advancement of Portuguese sailing along
the African coast, the distances traveled on the high seas, without
seeing land to rectify the position, were more extensive. The errors
associated with determining the direction and distance traveled become
accumulating over time. Thus, the positions obtained using only the
direction and estimates were affected by both errors were larger the
greater the interval of time to rectify the position. The Portuguese
solved this problem, even during the fifteenth century, astronomical
techniques adapted for use on board ships, techniques which allow a
thorough knowledge of the latitude of the ship. The letters began to
reflect the progress that has occurred in the Art of Sailing, to contain
an appropriate scale for determining the latitude of different places
Besides its main function would be to mark the positions
of ships at sea, the letters have other utility. They were represented
diverse information, or decorative purposes with a very strong practical
interest. Served, such as support for representation of images of
people, flora and fauna of the land that would be discovered. That is,
the letters were a way of representation of the exotic, these new
worlds, as the taste of the Renaissance man. Moreover, the letters were
included many of the elements that were used for the conduct of
navigation, such as graphs or tables of regulations and rules of
practice that the pilots are used to determine the elements of nautical
interest. In many of these views were still represented in some coastal
regions, or of political information such as the elements that gave
possession of a territory to a European kingdom.
The second limitation relates to the representation of a spherical surface a support plan. Since the Earth is approximately spherical shape without distorting its representation is only possible on a globe. In the sixteenth century was one of the assumptions used by the mapping. However, the use of balloons presents two major limitations. The first has to do with the size. As if a world is always the total land area the size would be large enough so that it can represent the surface in sufficient detail so that the world had any utility, which made it impractical to use. Furthermore, the measurement or the track of directions or distances on a sphere, vital to the knowledge of the vessel's position is rather complex, which is why the balloons never had any practical use at sea.
Pedro Nunes identified almost all the limitations that the letters of that time were represented in the earth's surface. He is the notion that the shortest distance between two points of the earth's surface is a curved line. Realized that the technique used to label directions in the letters implied that the meridians are parallel to each other, when in reality they all converge at the poles. Understood that this convergence due to a straight line represented a letter, or a direction to make always the same angle with all meridians does not correspond to a line on the surface of the globe but a spiral ending at the poles. The studies of Pedro Nunes had certainly influence the work that has a Mercator projection that has overcome these limitations of the letters of the time.
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