In
this article we are gonna looks at the problems surrounding systems of measurement
which grew up numerous hundreds of years, and looks at the introduction of the
metric system, and how SI unit of length "Meter" defined.
What is Measurement?
- Associating numbers with physical quantities
- Make one physical object as standard
for measurement purpose
- Compared another object with the
standard unit
- Compared data is the measurement
Length Measurement of Ancient Egyptian
- Based on human body
- Cubit as standard
- Developed around 300 BC
- 1 Cubit = length of an arm from the elbow to the extended fingertip
- Egyptians developed a standard royal cubit which was preserved in the form of a black granite rod against which everyone could standardize their own measuring rods
- For the measurement of shorter length other body parts are used
- The digit was the smallest basic unit, being the breadth of a finger
- 28 digit = 1 Cubit
- 4 Digit = 1 Palm
- 5 Digit = 1 Hand
- For measurement of smaller length than Digit Egyptian used unit fraction of Digit
- Based on Decimal Number System (½, 1/5, 1/10)
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| royal cubit |
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| credit : https://johnmanders.wordpress.com |
Length Measurement of Ancient Babylonian
- Developed around 1700 BC
- Base unit for length measurement = Cubit
- Babylonian Cubit (530 mm) slightly longer than Egyptian Cubit (524 mm)
- The Babylonian cubit was divided into 30 kus
- 1 kus = about a finger breadth
- Based on Hexadecimal Number system (1/2, 1/3 ¼ 1/6 1/12)
Length Measurement of Harrapan Civilization
- Developed between 2500 BC and 1700 BC
- Very precise scale and based on decimal system
- adopted a uniform system of weights and measures
- Unit of Length used in Ancient Indian Indus Valley Civilization, has been determined from the precise scale discovered by Ernest Mackay in the 1930-31 season excavation at Mohenjo-daro
- In Arthashastra, Chanakya mentions two types of Dhanushas as units for measuring lengths and distances.
- 1 Dhanusha = 96 Angulas
- 1 Garhpatya Dhanusha (used for road measurement) = 108 Angulas
- 1 Angulas = 16.764mm (very precise and uniform)
- A Yojana = 8000 Dhanusha (of 108 Angulas each) = 14.484096km = 9 miles, (exactly!).
- 1000 Dhanushas of 96 Angulas each = 1 mile
- Indus Inches = 1.32 Inches = 2 Angulas = 16.764mm
Length Measurement of Greek Civilization
- Greek Derived unit from Egyptian and Babylonian System
- Greeks used as their basic measure of length the breadth of a finger
- 16 finger = 1 foot
- 24 finger = 1 Greek Cubit
- Unit was not uniform, vary from state to state
Length Measurement of Roman Civilization
- The ancient Romans were sophisticated engineers, and consequently had well-defined units of measuring lengths and distances,
- The Romans adapted the Greek system
- Base unit was foot(pes)
- 1 foot = 12 inches
- 5 roman feet =1 pace(passus)
- 1000 pace = 1 Mile (mille passus)
- Local variation as roman spread
- Fathom originates from Danish people
- 1 fathom = distance between distance from fingertip to fingertip of outstretched arms
Disadvantage of Measurement System before Metric System
- Vary from place to place and time to time
- Not easy to convert from one unit to another unit
- Not suitable for Scientific Purpose and Industrial Purpose
Invention of Metric System
- Result of French revolution
- French sought to create a system that would endure “for all times, for all peoples.”
- To achieve this goal the French Academy of Sciences established a council of preeminent scientists and mathematicians, Jean-Charles de Borda, Joseph-Louis Lagrange, Pierre-Simon Laplace, Gaspard Monge and Nicolas de Condorcet, to study the problem in 1790
- The next year, they emerged with a set of recommendations. The new system would be
- a decimal system, that is, based on 10 and its powers
- To measure distance, the meter (derived from the Greek word metron, meaning “a measure”) should be considered as unit.
- The distance between the North Pole and the equator, with that line passing through Paris = 10,000,000 meter
- So 1 meter = (The distance between the North Pole and the equator)/10,000,000
- For Volume measurement Litre is would be used
- 1 L = volume of cube of 1/1000000 cum distrilled water
- 1 Kg = mass of 1 L distrilled water
- In 1792, astronomers Pierre Méchain and Jean-Baptiste Delambre set out to measure the meter by surveying the distance between Dunkirk, France, and Barcelona, Spain. After seven or so years of effort, they arrived at their final measure and submitted it to the academy, which embodied the prototype meter as a bar of platinum.
- It was later discovered that scientists made errors in calculating the curvature of the earth, and as a result the original prototype meter was 0.2 millimeters shorter than the actual distance between the North Pole and the equator. But the length of first prototype bar was accepted despite of its shortcomings
- With times more European countries adopted the French meter as their length standard
- However, while the copies of the meter bar were meant to be accurate, there was no way to verify this
- In 1875, the Treaty of the Meter, signed by 17 countries including the U.S., established the General Conference on Weights and Measures.
- The International Bureau of Weights and Measures (Bureau international des poids et mesures, BIPM), was also established at that time. Located just outside of Paris in Sèvres, France
- After first meeting, the BIPM ordered a new prototype
- Made up with platinum and iridium for better durablity
- have an X-shaped cross section to better resist distortions
- the meter would be defined as the distance between two lines inscribed on its surface
Wavelength Definition
- In 1960 the meter was redefined as 1,650,763.73 wavelengths of orange-red light, in a vacuum, produced by burning the element krypton (Kr-86)
- In 1873, James Clerk Maxwell suggested that light emitted by an element be used as the standard both for the metre and for the second. These two quantities could then be used to define the unit of mass
- In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson
Speed of light definition
- To further reduce uncertainty, the 17th CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of the second and the speed of light
- The metre is the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second.
- In 1984, the Geneva Conference on Weights and Measures has defined the meter as the distance light travels, in a vacuum, in 1/299,792,458 seconds with time measured by a cesium-133 atomic clock which emits pulses of radiation at very rapid, regular intervals.
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