See also the home page for Contents and a search facility for this site.
See also the home page for Contents and a search facility for this site.
www.technology1.co.uk
I find it surprising that the ancient greeks over 2000 years ago had people who had better understanding of mathematics than perhaps the majority of the population of the western world.
Pythagoras c 580 BC to c. 500 BC
Aristotle 384 BC to 322 BC
Euclid c. 300 BC
Progress in scientific knowledge seemed to stop until around 1600 when the principal thinkers were mainly in the more northern parts of Europe.
Galileo 1564 to 1642 was a major pioneer in scientific thinking.
Mathematics started to emerge into its modern form, and be applied to the physical world.
Descartes, 1596-1650 was mainly regarded as a philosopher, but also did pioneering work in mathematics including algebra and geometry. Cartesian coordinates are named after him.
Sir Isaac Newton 1642 to 1727 made a giant leap of understanding in physics. He introduced precise concepts of mass and force and discovered three fundamental laws of motion:
(1) The momentum of an object is constant unless an outside force acts on the object.
(2) The rate of change of the momentum of an object is proportional to the force acting on it.
(3) For every action there is an equal and opposite reaction.
I have heard it said that we now take these things for granted, but I don't think so. Most non-scientific people even in the modern world do not see these things easily. It is intuitive from our everyday experience that moving things slow down and eventually come to rest. There is the feeling that the weight of an object determines how much force will be needed to move it. Insufficient force will not move it at all, and if the force is sufficient, the amount of the force will (in some vague way) determine either the speed of movement, or how far it moves. All of these are wrong, and Newton knew it.
Newton also discovered that white light is made up of a mixture of lights of different colours. It was previously thought that white light was pure and indivisible and only being modified when split into colours by a prism.
Newton was committed to the certainty of knowledge and observed that a small amount of certainty was worth more than a large amount of uncertain knowledge.
Newton was born a little after the time of Elizabeth I and Shakespeare, and lived through the English Civil War and the Plague.
Contemporaries of Newton in Britain were Robert Hooke and Robert Boyle.
Hooke did some pioneering work with early microscopes.
Hooke's Law states that the deformation of a spring is proportional to the force applied.
Boyle's Law states that the volume of a fixed quantity of air is inversely proportional to its pressure (at a constant temperature).
Aristotle's ancient theory that everything was made of four elements (earth, air, fire, and water) was only now beginning to be discredited.
Boyle also recognised that sound is transmitted through air, and will not be transmitted in a vacuum.
The Royal Society of London for the Promotion of Natural Knowledge was founded around 1660-1662 and granted a charter by the new king Charles II after the monarchy was restored after the time of Cromwell. It is good to see that even in those days scientists were honoured and appreciated by the establishment, and got good remuneration for their efforts.
Static electricity was known about in 1745, and the Leyden jar was invented that year. Probably named after the University of Leiden in Holland. Early methods of generating static electricity were haphazard. The Wimshurst machine was invented much later, in 1879 by James Wimshurst 1832 to 1903. British. The Van de Graaff generator was later still, invented by Van de Graaff, USA. 1901-1967.
Volta, Italian, 1745 to 1827 invented the electric battery in 1800 and the first source of continuous electric current. This was the time of Napoleon. The unit Volt is named after him. (Not to be confused with Voltaire, 1694 to 1778, the French writer!).
Ohm, German, 1789 to 1854. Recognised that the current through a resistor is proportional to the applied voltage. The ratio of the voltage to the current defines the resistance and the unit of resistance was named after him. This is essentially Ohms Law, one of the most fundamental principles used in electronics, but surprisingly not always properly understood by some electronics engineers. For example, it only applies to resistors. Also if the current is the thing which is controlled and applied, the voltage will be forced to appear across the resistor in accordance with the law.
Ampere, French, 1775 to 1836. Regarded as the founder of electromagnetism. Invented a type of ammeter. The unit of current, the ampere or amp was named after him.
Michael Faraday 1791 to 1867 discovered the relationship between electricity and magnetism and invented the electric generator. Previously electricity had only been produced by chemical action, i.e. batteries. The Farad, the unit of capacitance was named in his honour.
The electric telegraph was made possible by invention of batteries, and by Orsted's discovery that a moving needle could indicate an electric current. The first practical telegraph systems were invented in 1837. Two systems were invented independently around the same time. One by Sir William Fothergill Cooke and Sir Charles Wheatstone in Britain. This used 5 signal wires sending analogue currents to indicate letters on meters. Also in 1837 Morse, in New York, invented a different system using dots and dashes. This needed only two wires.
James Clerk Maxwell, Scottish, 1831 to 1879 built upon the work of Faraday to further the knowledge of electromagnetic theory.
Maxwell was the first to recognise the concept of electromagnetic radiation and paved the way for quantum theory. The Maxwell, a unit of magnetic flux is named after him. Later, in 1931, Einstein described the understanding arising from Maxwell's work as "the most profound and the most fruitful that physics has experienced since the time of Newton."
Alexander Graham Bell 1847 to 1922. Born in Scotland.
Bell was more of a 'sound man' than an 'electronics man'. He had a background of working as a teacher in speech and elocution. He went to the USA and developed the telephone there and was granted a patent for the telephone on the 7th March 1876. The decibel was named after him.
Heinrich Hertz, 1857 to 1894, German, was the first to transmit and receive radio waves. He studied the work of Maxwell and investigated radio waves in 1885 to 1889. The unit of frequency, the hertz, was later named after him. Not to be confused with dramatist Henrik Hertz or physicist Gustav Hertz (who was Heinrich's nephew).
Marconi, 1874 to 1937, started experimenting with radio communication in 1894. He gradually improved the technology of radio, working partly in Italy and partly in Britain. This was wireless telegraphy, not speech. A system for using multiple wavelengths was developed.
Edison was one of the first to notice the phenomenon that under certain conditions a current would pass between electrodes in a vacuum tube, but did not develop it further. This is known as the Edison effect.
English physicist Sir J. J. Thomson (Joseph John) did some work on this around 1897. English electrical engineer (Sir) John Ambrose Fleming designed a tube called a diode which could rectify an alternating current and hence had application in detection of radio waves. It was patented in 1904.
The great breakthrough which made amplification possible was when the American Lee De Forest developed the diode further in 1906 by adding a third electrode (later called the grid). This was the first triode and was patented in 1907. He called it the Audion.
Picture of an Audion.
Note the similarity with an electric light bulb and the Edison screw fit for the connections to the filament.
It seems that de Forest was not seeking to achieve amplification. He was experimenting on ways of improving the detection of radio waves.
The diode had been applied in radio receivers and initially the audion was used similarly, but as a kind of enhanced detector. One account says "For some years the audion was used only as a detector for radio telegraphy".
Later De Forest realised the potential of the audion as an amplifier. A small electrical signal on the grid could control a larger signal through the valve. One of the first applications was as a repeater for long distance communications.
The next important step was made by Fritz Lowenstein (USA). He found that
adding a negative bias to the grid improved the performance significantly. It
was probably Lowenstein who developed the first audio amplifier as a result
of this in about 1911. Early electrical engineer Lloyd Espanchied said in 1973,
"Fritz Lowenstein, here in New York, had early in 1911 made De Forest's
audion into an amplifier before De Forest ever did".
Click here to see the circuit diagram of an early audio amplifier
See also The History of Sound Recording on this site.
Ampere or Amp. The current which causes a force of 2 
10-7 newton per metre of length when applied to two conductors one
metre apart.
Bel and Decibel. A means of expressing power ratios, primarily for sound. Named after Alexander Graham Bell. The Bel is the log (to base 10) of the power ratio, and a decibel is one tenth of this.
Coulomb. The amount of electricity which passes in one second at the rate of one ampere. (Conversely, one ampere is one coulomb per second).
Farad. The capacitance which will store one coulomb of electricity when the potential applied is one volt.
Gramme or Gram. Arbitrarily defined originally as the mass of one cubic centimetre on water (though this is not exact). Forms the basis of many other units.
Joule. The work done by one newton acting through one metre.
Maxwell. A unit of magnetic flux.
Metre. Arbitrarily defined as a fraction of the circumference of the earth. Forms the basis of many other units.
Newton. The force which gives a mass of one kilogram an acceleration of one metre per second per second. (One newton is equal to a force of 100,000 dynes).
Ohm. The resistance of a circuit in which a potential difference of one volt produces a current of one ampere.
Second. Arbitrarily defined as a fraction of a day. Forms the basis of many other units.
Volt. Defined as the difference in potential between two points in a conductor carrying one ampere of current when the power dissipated between the points is one watt. It is equivalent is the potential difference across a resistance of one ohm when one ampere is flowing through it.
Watt. A unit of power equal to one joule per second. Power is the rate of doing work.
It is interesting to see the relationship between different units. The gramme is related to the centimetre through the density of water, but this is only an arbitrary choice. There is nothing fundamental about the density of water. The watt is more interesting. It is derived primarily from mechanics, but as a unit of power it also applies to electricity. It is used as the way of obtaining the definition of the volt, and hence the ohm. In fact the watt is the power which arises when one volt is applied across a resistance of one ohm, but it is important not to define it this way.
Energy is the capacity to do work and so takes the same units, e.g. joules. A joule is one watt.second, or the work done in one second at a rate of power equal to one watt. A more common unit of energy in everyday life is the kilowatt.hour which is clearly 1000 x 60 x60 joules.
The concepts of work and power are often confused.
This site is written by S. J. Farthing, Portsmouth, England.
My personal site and e-mail address are at: www.farthing.me.uk