Longitude
Created | Updated Jan 28, 2002
Introduction
Longitude... It plays a vital role in many areas of everyday
life, and yet, it was considered impossible to discover back
in the 18th century, when it was desperately needed for
navigation.
This is my shot at explaining the phenomenon "Longitude" in
an easily comprehendable way. It hasn't been talked about
in the h2g2 (as far as I know), expect for a question on the
Ask H2G2 forum, which gave me the idea to write this article.
If you just want to know the facts, read the section titled
"The Essence". If you have more time and are interested in
the problem, you may want to read the other sections as well,
which describe the development of the longitude problem up to
its final solution by John Harrison.
The Essence
To get started, I'll explain what longitude is in the first
place, even at the risk that you already know it. If you
do, feel free to skip the section "Basics".
The planet Earth is a sphere (surprise, surprise...
). I know you
know, but I must make the point, and the point is that
conventional coordinate systems, as the Cartesian
coordinates1, don't fit and
can't be used to specify points on Earth's surface. So a
new type of coordinates had to be invented: Longitude and
Lattitude.Lattitude
The business with the lattitude was much easier, because
the origin is given by Nature - the Equator, the line which
has the greatest distance from Earth's axis of rotation.
I was generally agreed upon that the Equator was to be 0
degrees of lattitude. The other degrees of lattitude, called
Parallels, were defined as a series of shrinking concentric
rings, oriented just like the Equator, which grow smaller
and smaller and reach virtually zero size at the poles,
where we have 90 degrees of lattitude.Longitude
The lines of longitude, or Meridians, are defined in another
way. They are lines that loop from the North Pole to the
Southand back again in great, equal-sized circles, that is,
they all have the same length, but the distance between
them changes - from sixty-eight miles per degree of
longitude on the Equator to their points of intersection,
the poles.
In order to navigate a ship safely, a seaman needs to know
its position on the surface of the Earth, that is, its
coordinates in longitude and lattitude. While the lattitude
is easily obtained by measuring the length of the day or
the height of the sun, the moon or certain stars. This is
a very old method, and even Columbus used it to sail to
"India", by staying on the same parallel.
Longitude can't be obtained that easy. The method that is
considered the most reliable and practicable is by using
a chronometer which keeps the local time at a point of known
longitude, say, the home port of the ship. By judging the
local time of the ship2, the
navigator computet the time difference between home port
and ship. Because good old Earth does one full rotation
(360 degrees) in 24 hours, one hour corresponds to 360 /
24 = 15 degrees. One hour time difference from the home
port means 15 degrees longitude difference (east or west).
Having determined lattitude and longitude in the described
ways, the ship's captain knew where he was and in which
direction he had to sail.
The problem of defining coordinates for Earth's surface is an
old one. The first known occurence of lattitude and longitude
is at least 3 centuries B.C. The ancient Greek cartogtapher
and astronomer Ptolemy introduced these imaginary lines to his
27-map world atlas, around 150 A.D. The origin of lattitude he
used was the Equator, which he determined by observing the
motions of the celestial bodies, while nature had not provided
him with a mark for 0 degrees longitude. He chose the Canary
and Madeira Islands for this purpose, rather arbitrarily.
As already stated above, finding Lattitude on sea was as easy
as comparing the length of the day with astronomical tables
provided for this purpose. Longitude, which depends on
knowing the exact time on two places on Earth, was impossible
to discover, because no clock or timekeeper was precise enough
on land, let alone the rolling ship with strongly varying
temperature, atmospheric pressure, and slight changes of the
Earth's gravity, which made the clocks run faster or slower,
rendering them unusable for navigating purposes.
A series of ship collisions caused by not knowing the exact
longitude forced the King, Charles II, to take action. In
1676, the Royal Observatory in Greenwich was founded, with
the explicit purpose for the astronomers to
The first Astronomer Royal was John Flamsteed, a young man who
wanted to predict the moon's motion against the stars and spent
all his life in mapping their positions. His excellent star
catalog was published in 1725, but it was no solution for the
Longitude dilemma, because the movement of the moon wasn't
fully understood at the time.
Great Britain was well aware of this problem. A nation of
seafarers, with the strongest navy at the time, wasn't able
to keep track of its ships' positions. This was brought to
the attention of the general public in 1707, when four
English warships, returning victorious from a sea battle
with the French fleet at Gibraltar, misjudged their
longitude and, sailing northward, collided with the Scilly
Islands. 2,000 men died, among them Admiral Sir Clowdisley
Shovell, and that was not the first accident of that kind.
The government was forced to act. In 1714, it passed
the "Longitude Act", stating that a reward of 20,000 pounds,
a king's ransom, was to be awarded to anyone who found a
practicable solution to the longitude problem.
From then on, many curious and dubious so-called solutions
were sent to the Longitude Board, only to be rejected. To
name them all would take up too much time and space, but the
more interesting are listed in the dection "Curious
Proposals".
John Harrison, the man who solved the longitude problem, was
born in 1693, as the fifth child of a carpenter. Little is
known about his childhood. He became a clockmaker, though
apparently he didn't have a teacher. All he knew, he had
taught himself, yet he had acquired quite a reputation as a
watchmaker, and had also build a tower clock. When he first
heard about the Longitude Prize around 1726, he realized that
making his fine clocks seaworthy could make him rich and
famous. The rest of his life he spent developing marine
timekeepers.
He had an inventive mind, and thought of ways to render a
pendulum, which was useless on a rolling ship obsolete, how
to make a clock less subject to temperature differences and
how to minimize friction in his clockworks. In 1937, he
presented his first marine tiekeeper, Harrison-1 or H-1 for
short, to the Longiude Board. The test journey to the West
Indies proved that the clock entitled Harrison to claim the
20,000, but he was too much of a perfectionist to do so. He
said that he could make the clock run even more precisely,
and that he would come back with the second clock. He only
took a little amount of money to cover his expenses.
In 1741, he presented H-2, but he was disgusted with it. He
said that he could do much better and asked for more money
and time. After being granted both, he retreated to his
workbench for 18 years. At the end of this period, in 1758,
he came up with H3, which he considered his masterpiece.
However, it was never tested on sea - first because of the
7-years war (Nobody would risk losing this precious item on
a sea battle), and then because Harrison had already made
its successor - H-4, completed 1760.
H-4 was very different from its predecessors. Harrison
called it "The Watch". It was the first that was designed
to be small and easy to handle, in contrast to H-1 to H-3,
which had all required cases of about 2ft * 2ft * 2ft.
As required by the Longitude Act, the Watch was tested on a
transatlantic voyage at the end of 1761 and the beginning
of 1762. The results achieved were sensational - on the
journey across the ocean, with fine sailing weather, it
lost as little as 5 seconds, and on the journey back, with
heavy storms and high waves, the loss was less than 2
minutes. This was precise enough (according to the
Longitude Act) to claim the 20,000 pounds, but the Board
of Longitude was reluctant and asked Harrison to explain
the mechanism, which he refused. Then the Board decided
that a second trial voyage should be made, and in 1764,
H-4 sailed to the West Indies, performing 3 times better
than required by the Longitude Act. Now, there was no
denying Harrison's deserving the reward, nevertheless
the Board set up a couple of conditions. Harrison was to
have half the prize, 10,000 pounds, for all four
timekeepers he had constructed, and for H-4's plans. If
he wanted the rest of the money, he had to build two
duplicates of H-4, to prove that it could be duplicted.
In 1770, John Harrison finished the first copy, H-5. He
was gettint older, and it was to be doubted that he
could make another watch. Then, in 1772, his son William
wrote an emotional letter to King George III, describing
his father's hardship. The King agreed to test H-4
himself, and after a year of succesful trial at the Royal
Observatory in Greenwich, he ordered Harrisson to be
awarded another 8,750 pounds. That still wasn't the full
sum, but Harrison was content. He died on his 83rd
birthday, 24 March 1776.
Curious Proposals
After the prize for discovering Longitude at sea was set
up, many creative minds tried to solve this problem, and
the Board of Longitude was forced to reject many
proposals. Some of them are so curious that they deserve
special mention.
In Paris, there was an alchemist who claimed he had
invented a magical healing powder. When applied to a
piece of clothing that had been in contact with a wound,
it would cause that wound to close, but also considerable
pain to the injured person.
The idea was simple. A wounded dog was taken on board the
ship. Every day at noon in Greenwich, a reliable person
appplied the powder to a strip of clothing that had been
in contact with the wound, causing the dog to howl up with
pain. Thus, the navigator would know the exact time at
Greenwich, rendering a timekeeper obsolete. Of course,
the dog had to be wounded every day, so that the wound
couldn't heal.
Another proposal was to anchor many ships at strategic
positions in the oceans, probably 7 miles apart from
each other, who could announce the exact time by firing
their cannons.
This was rejected, mostly because of the cost involved,
but also because the ships weren't safe from pirates,
and the sailors on the ship would be worse off than a
lighthouse keeper.
Astronomy was able to predict eclipses of the Sun and
the Moon fairly precisely at the time, so it was
suggested that such events be used to determine the
exact time.
The problem was that they occured much too rarely to be
of any use.
The idea for this solution is Gallileo Gallilei's. He
observed Jupiter's moons, noticing that eclipses ocurred
very often, several times a day. He figured that if it
was possible to predict the events with sufficient
precision, they could be used to discover exact time.
This method was considered the main rival of the time
keeper method, and was used succesfully on land, but on
sea, it had several drawbacks. The rolling of the ship
made it nearly impossible to keep a telescope on Jupiter
for any period of time, and even when the sea was calm
and the sky clear, it took as much as 4 hours to do the
necessary computations. That is why this method couldn't
succeed.
Sources of Information
Before writing this entry, I consulted quite a few
encyclopaedias, like the Encyclopaedia Britannica,
Microsoft's Encarta, and the Encyclopaedia Galactica.
Much of the information is taken from Dava Sobel's
excellent book, "Longitude", which is a recommendable
read to anyone interested in the topic.
Last but not least, the website of Greenwich, the
Maritime Museum and the Old Royal Observatory were
very helpful.
Longitude... It plays a vital role in many areas of everyday
life, and yet, it was considered impossible to discover back
in the 18th century, when it was desperately needed for
navigation.
This is my shot at explaining the phenomenon "Longitude" in
an easily comprehendable way. It hasn't been talked about
in the h2g2 (as far as I know), expect for a question on the
Ask H2G2 forum, which gave me the idea to write this article.
If you just want to know the facts, read the section titled
"The Essence". If you have more time and are interested in
the problem, you may want to read the other sections as well,
which describe the development of the longitude problem up to
its final solution by John Harrison.
The Essence
The Basics
To get started, I'll explain what longitude is in the first
place, even at the risk that you already know it. If you
do, feel free to skip the section "Basics".
The planet Earth is a sphere (surprise, surprise...
know, but I must make the point, and the point is that
conventional coordinate systems, as the Cartesian
coordinates1, don't fit and
can't be used to specify points on Earth's surface. So a
new type of coordinates had to be invented: Longitude and
Lattitude.Lattitude
The business with the lattitude was much easier, because
the origin is given by Nature - the Equator, the line which
has the greatest distance from Earth's axis of rotation.
I was generally agreed upon that the Equator was to be 0
degrees of lattitude. The other degrees of lattitude, called
Parallels, were defined as a series of shrinking concentric
rings, oriented just like the Equator, which grow smaller
and smaller and reach virtually zero size at the poles,
where we have 90 degrees of lattitude.Longitude
The lines of longitude, or Meridians, are defined in another
way. They are lines that loop from the North Pole to the
Southand back again in great, equal-sized circles, that is,
they all have the same length, but the distance between
them changes - from sixty-eight miles per degree of
longitude on the Equator to their points of intersection,
the poles.
Finding the Position
In order to navigate a ship safely, a seaman needs to know
its position on the surface of the Earth, that is, its
coordinates in longitude and lattitude. While the lattitude
is easily obtained by measuring the length of the day or
the height of the sun, the moon or certain stars. This is
a very old method, and even Columbus used it to sail to
"India", by staying on the same parallel.
Longitude can't be obtained that easy. The method that is
considered the most reliable and practicable is by using
a chronometer which keeps the local time at a point of known
longitude, say, the home port of the ship. By judging the
local time of the ship2, the
navigator computet the time difference between home port
and ship. Because good old Earth does one full rotation
(360 degrees) in 24 hours, one hour corresponds to 360 /
24 = 15 degrees. One hour time difference from the home
port means 15 degrees longitude difference (east or west).
Having determined lattitude and longitude in the described
ways, the ship's captain knew where he was and in which
direction he had to sail.
1Cartesian coordinates are the
"normal" coordinates that you used
in school, two axises (x and y) form a right angle and
points are specified by giving their offset from a point of
origin in the x and y directions.2Local noon is when the sun
reaches the highest point of its path
The Quest for Longitude"normal" coordinates that you used
in school, two axises (x and y) form a right angle and
points are specified by giving their offset from a point of
origin in the x and y directions.2Local noon is when the sun
reaches the highest point of its path
Ancient Attempts
The problem of defining coordinates for Earth's surface is an
old one. The first known occurence of lattitude and longitude
is at least 3 centuries B.C. The ancient Greek cartogtapher
and astronomer Ptolemy introduced these imaginary lines to his
27-map world atlas, around 150 A.D. The origin of lattitude he
used was the Equator, which he determined by observing the
motions of the celestial bodies, while nature had not provided
him with a mark for 0 degrees longitude. He chose the Canary
and Madeira Islands for this purpose, rather arbitrarily.
Problems with Longitude
As already stated above, finding Lattitude on sea was as easy
as comparing the length of the day with astronomical tables
provided for this purpose. Longitude, which depends on
knowing the exact time on two places on Earth, was impossible
to discover, because no clock or timekeeper was precise enough
on land, let alone the rolling ship with strongly varying
temperature, atmospheric pressure, and slight changes of the
Earth's gravity, which made the clocks run faster or slower,
rendering them unusable for navigating purposes.
The Old Royal Observatory
A series of ship collisions caused by not knowing the exact
longitude forced the King, Charles II, to take action. In
1676, the Royal Observatory in Greenwich was founded, with
the explicit purpose for the astronomers to
"apply the most exact Care and Diligence
to the rectifying of the Tables of the Motions of the Heavens,
and the Places of the fixed Stars, so as to find out the
so-much desired Longitude at Sea, for perfecting the Art of
Navigation"
The first Astronomer Royal was John Flamsteed, a young man who
wanted to predict the moon's motion against the stars and spent
all his life in mapping their positions. His excellent star
catalog was published in 1725, but it was no solution for the
Longitude dilemma, because the movement of the moon wasn't
fully understood at the time.
The Longitude Act
Great Britain was well aware of this problem. A nation of
seafarers, with the strongest navy at the time, wasn't able
to keep track of its ships' positions. This was brought to
the attention of the general public in 1707, when four
English warships, returning victorious from a sea battle
with the French fleet at Gibraltar, misjudged their
longitude and, sailing northward, collided with the Scilly
Islands. 2,000 men died, among them Admiral Sir Clowdisley
Shovell, and that was not the first accident of that kind.
The government was forced to act. In 1714, it passed
the "Longitude Act", stating that a reward of 20,000 pounds,
a king's ransom, was to be awarded to anyone who found a
practicable solution to the longitude problem.
From then on, many curious and dubious so-called solutions
were sent to the Longitude Board, only to be rejected. To
name them all would take up too much time and space, but the
more interesting are listed in the dection "Curious
Proposals".
John Harrison
John Harrison, the man who solved the longitude problem, was
born in 1693, as the fifth child of a carpenter. Little is
known about his childhood. He became a clockmaker, though
apparently he didn't have a teacher. All he knew, he had
taught himself, yet he had acquired quite a reputation as a
watchmaker, and had also build a tower clock. When he first
heard about the Longitude Prize around 1726, he realized that
making his fine clocks seaworthy could make him rich and
famous. The rest of his life he spent developing marine
timekeepers.
He had an inventive mind, and thought of ways to render a
pendulum, which was useless on a rolling ship obsolete, how
to make a clock less subject to temperature differences and
how to minimize friction in his clockworks. In 1937, he
presented his first marine tiekeeper, Harrison-1 or H-1 for
short, to the Longiude Board. The test journey to the West
Indies proved that the clock entitled Harrison to claim the
20,000, but he was too much of a perfectionist to do so. He
said that he could make the clock run even more precisely,
and that he would come back with the second clock. He only
took a little amount of money to cover his expenses.
In 1741, he presented H-2, but he was disgusted with it. He
said that he could do much better and asked for more money
and time. After being granted both, he retreated to his
workbench for 18 years. At the end of this period, in 1758,
he came up with H3, which he considered his masterpiece.
However, it was never tested on sea - first because of the
7-years war (Nobody would risk losing this precious item on
a sea battle), and then because Harrison had already made
its successor - H-4, completed 1760.
H-4 was very different from its predecessors. Harrison
called it "The Watch". It was the first that was designed
to be small and easy to handle, in contrast to H-1 to H-3,
which had all required cases of about 2ft * 2ft * 2ft.
As required by the Longitude Act, the Watch was tested on a
transatlantic voyage at the end of 1761 and the beginning
of 1762. The results achieved were sensational - on the
journey across the ocean, with fine sailing weather, it
lost as little as 5 seconds, and on the journey back, with
heavy storms and high waves, the loss was less than 2
minutes. This was precise enough (according to the
Longitude Act) to claim the 20,000 pounds, but the Board
of Longitude was reluctant and asked Harrison to explain
the mechanism, which he refused. Then the Board decided
that a second trial voyage should be made, and in 1764,
H-4 sailed to the West Indies, performing 3 times better
than required by the Longitude Act. Now, there was no
denying Harrison's deserving the reward, nevertheless
the Board set up a couple of conditions. Harrison was to
have half the prize, 10,000 pounds, for all four
timekeepers he had constructed, and for H-4's plans. If
he wanted the rest of the money, he had to build two
duplicates of H-4, to prove that it could be duplicted.
In 1770, John Harrison finished the first copy, H-5. He
was gettint older, and it was to be doubted that he
could make another watch. Then, in 1772, his son William
wrote an emotional letter to King George III, describing
his father's hardship. The King agreed to test H-4
himself, and after a year of succesful trial at the Royal
Observatory in Greenwich, he ordered Harrisson to be
awarded another 8,750 pounds. That still wasn't the full
sum, but Harrison was content. He died on his 83rd
birthday, 24 March 1776.
Curious Proposals
After the prize for discovering Longitude at sea was set
up, many creative minds tried to solve this problem, and
the Board of Longitude was forced to reject many
proposals. Some of them are so curious that they deserve
special mention.
The Wounded Dog Method
In Paris, there was an alchemist who claimed he had
invented a magical healing powder. When applied to a
piece of clothing that had been in contact with a wound,
it would cause that wound to close, but also considerable
pain to the injured person.
The idea was simple. A wounded dog was taken on board the
ship. Every day at noon in Greenwich, a reliable person
appplied the powder to a strip of clothing that had been
in contact with the wound, causing the dog to howl up with
pain. Thus, the navigator would know the exact time at
Greenwich, rendering a timekeeper obsolete. Of course,
the dog had to be wounded every day, so that the wound
couldn't heal.
The Anchored Ships Method
Another proposal was to anchor many ships at strategic
positions in the oceans, probably 7 miles apart from
each other, who could announce the exact time by firing
their cannons.
This was rejected, mostly because of the cost involved,
but also because the ships weren't safe from pirates,
and the sailors on the ship would be worse off than a
lighthouse keeper.
The Solar/Lunar Eclipse Method
Astronomy was able to predict eclipses of the Sun and
the Moon fairly precisely at the time, so it was
suggested that such events be used to determine the
exact time.
The problem was that they occured much too rarely to be
of any use.
The Jupiter's Moons Eclipse Method
The idea for this solution is Gallileo Gallilei's. He
observed Jupiter's moons, noticing that eclipses ocurred
very often, several times a day. He figured that if it
was possible to predict the events with sufficient
precision, they could be used to discover exact time.
This method was considered the main rival of the time
keeper method, and was used succesfully on land, but on
sea, it had several drawbacks. The rolling of the ship
made it nearly impossible to keep a telescope on Jupiter
for any period of time, and even when the sea was calm
and the sky clear, it took as much as 4 hours to do the
necessary computations. That is why this method couldn't
succeed.
Sources of Information
Before writing this entry, I consulted quite a few
encyclopaedias, like the Encyclopaedia Britannica,
Microsoft's Encarta, and the Encyclopaedia Galactica.
Much of the information is taken from Dava Sobel's
excellent book, "Longitude", which is a recommendable
read to anyone interested in the topic.
Last but not least, the website of Greenwich, the
Maritime Museum and the Old Royal Observatory were
very helpful.
1Cartesian coordinates are the
"normal" coordinates that you used
in school, two axises (x and y) form a right angle and
points are specified by giving their offset from a point of
origin in the x and y directions.2Local noon is when the sun
reaches the highest point of its path
"normal" coordinates that you used
in school, two axises (x and y) form a right angle and
points are specified by giving their offset from a point of
origin in the x and y directions.2Local noon is when the sun
reaches the highest point of its path
