2nd Group Seeking The Longitude

2nd Group 09 何元輝 17吳昭瑩 18吳璟淇 41 徐千甯

Seeking the longitude Latitude and longitude: defining positions on the Earth’s surface It had probably come into use in ancient Greece before 300 BC, but it’s different from we think of today

Claudius Ptolemy( c. AD 100-165 ) The first person to offer a mathematically clear theory of geographical latitude and longitude Two major works: 1.Great Collection or Megale Syntaxis, better known as the Almagest 2.Geography, a gazetteer and atlas of the known world in eight books

Hipparchos He suggests making use of the eclipses of the Moon, but he failed 1.Because the Sun must be below the horizon during a lunar eclipse, a sundial cannot be used 2.eclipses are comparatively rare in any one place 3.defining a particular point in an eclipse is not easy

The age of discovery Under the leadership of Prince Henry, the Portuguese push to the southward was intensified The Portuguese found a seaway to the East by sailing southward and eastward round Africa The Portuguese succeeded in devising methods and instruments to find latitude by observation of the Pole Star and of the Sun

First Method for seeking Longitude

To find out the longitude by The Lunar Distance a.1514 Johann Werner of Nuremberg publish a new translation of the First Book of Ptolemy’s Geography.

b. Using a cross-staff (page22&23-picture)

How to use the way? a. The Moon appears to move comparatively quickly against the background of the stars in the zodiac belt. b. The distance between the Moon and a fixed star which is little or not away from the ecliptic. c. The astronomical tables for the stars’ positions. d. An almanac for the Moon’s predicted position.

However, it was only theory. Tables and cross-staff were not accurate. b. Lunar parallax

Second Method for seeking Longitude

Gemma Frisius Born: 8 Dec 1508 in Dokkum, Friesland, The Netherlands Died: 25 May 1555 in Louvain, Brabant (now Belgium)

Invented by Gemma Frisius De Principiis Astronomiae Cosmographicae(1530,Louvain) Chapter 19 ‘Concerning a new method of finding longitude’

... it is with the help of these clocks and the following methods that longitude is found. ... observe exactly the time at the place from which we are making our journey. ... When we have completed a journey ... wait until the hand of our clock exactly touches the point of an hour and, at the same moment by means of an astrolabe... find out the time of the place we now find ourselves. ... In this way I would be able to find the longitude of places, even if I was dragged off unawares across a thousand miles.

astrolabe

As early as 1522, Gemma Frisius proposed a solution to the problem of longitude using a timepiece . At this time however, mechanical clocks lacked the consistency necessary to make accurate measurements of time. While many inventors struggled to perfect the chronometer, many other solutions were proposed to the problem of longitude including lunar eclipses and magnetic declination.

Chronometer John Harrison in 1761 built a marine chronometer with a spring and balance wheel escapement. It kept time on board a rolling ship to about one-fifth of a second a day during sea trials in 1762. This Chronometer gave the means of determining longitude to within one-half degree. The British Board of Longitude announced an awarded of 20,000 pounds in 1714 for an accurate chronometer for determining longitude on board a ship at sea. However, it required the aid of King George III to intervene in 1773 for the money to be given to Harrison.

                   Harrison's No. 4 Chronometer

The History of the Longitudinal Problem Spain and Portugal The determination of longitude became a serious problem in the end of 16th century. King Phillip III (1578-1621) of Spain proposed an international contest to solve the problem of longitude at sea . The winner would receive 6000 ducats plus an additional 2000 ducats per year for life.

In 1600, the States General of the Dutch Republic offered a reward of 5000 florins, later increased to 15000 in 1611 to the person who solved the problem of longitude.

Galileo Galilei Born: 15 Feb 1564 in Pisa (now in Italy) Died: 8 Jan 1642 in Arcetri (near Florence) (now in Italy)

Galileo and the Problem of Longitude

Galileo and the Medicean Stars Galileo discovered the moons of Jupiter on January 7, 1610. Galileo realized repeated rotations of Jupiter's moons is a solution to the longitude problem since the moons of Jupiter acted as type of universal clock.

Suppose Galileo observed the configuration above in Rome. Same configuration of Jupiter's moons is observed in Greenwich England The local time difference between the two cities was recorded as 48 minutes, Rome would be located at 12o E of Greenwich. This method also required a method for determining local time.

Seventeenth-century developments In 1637, Galileo demonstrated the first pendulum as a controller for clock Control by gravity It has a natural frequency that is independent of amplitude and weight of the bob Its frequency is related only to length of the pendulum and acceleration of gravity.

20 years later, in 1657, Christian Huygens invented the first weight-driven clock with a pendulum

Increase the accuracy in time-keeping In 1670s, he also invented the balance spring for watches

In 1657, Huygens started to produce the first marine timekeeper Early stage- use pendulum In 1674 use balance and balance spring 100 years later, a satisfactory marine timekeeper is made

In 17th century, many scientists wanted to find the longitudes France is larger in the map than it is actually is. The king is displeased and said, “His surveyors had lost him more land than his armies had gained.”

References http://www.stanford.edu/group/shl/Eyes/Jovilabe/history.html http://www.ernie.cummings.net/clock.htm#LONG