Introduction

The machine

The story

Static history

The challenge

For teachers

For reference

A short history of electrostatics.

In 1769 Priestley's electrostatic machine machine was described in the second edition of  his 'History and Present State of Electricity'. In this book Priestley presents a timeline of discoveries in the the area of electrostatics, and puts forward his own ideas.

Below is a simple list of achievements in the study of electrostatics. There is a challenge associated with each person. If you are taking part in the Priestley Physics Project you will be assigned a person and the associated activity to perform. To view the activity, click on the relevent task number.

 

Task 1

If we rub a plastic pen with a dry cloth it will pick up pieces of paper and other small objects.  If a balloon is rubbed on our clothes it will stick to a wall. Knowledge of this effect goes back to the 6th century B.C. when the Greek philosopher Thales noticed that if he rubbed and polished a lump of amber it would attract small objects.

 

Task 2

William Gilbert made an extensive study of the effects of both magnetism and electricity in the 16th century.  He was, perhaps, the first person to explain some of the differences.  He invented the first electrical instrument called a versorium, a simple pointer which was attracted to charged objects. 

Task 3

The German, Otto von Guericke  built a machine to produce large amounts of static electricity.  It consisted of a large ball of sulphur, which he could spin in a simple wooden frame.  He was able to produce enough static electricity to make a  spark.

Task 4

Francis Hauksbee used a glass globe as an electrical generator, instead of the sulphur ball used by von Guericke.  In 1709 he  he placed a small amount of mercury into a flask, removed the air, and then charged the glass by friction. The flask  produced a strange glow.  This effect was used much later in the construction of fluorescent lighting and the neon lamp.

 

Task 5

Stephen Grey was the first to realise that static electricity (electricity that is standing still) could be made to flow along an object.  He explained that some materials were conductors of electricity and that others were insulators.  He also was the first to point out the importance of ‘earthing’ in explaining electrostatic effects.  He found that a metal object is difficult (but not impossible) to charge by friction because, being a conductor, the electricity easily flows off the object and down to the earth.

 

 

Task 6

For a time, electricity was thought to be a kind of fluid.  Charles Dufay was the first to notice both the attractive and repulsive effects of static electricity and concluded correctly that there were two types of electricity.  Dufay also suggested that all objects contained electricity. 

Benjamin Franklin gave us the modern terms of positive and negative.  His idea was that an object that has excess electricity is called positive, if it has a deficit we call it negative and an uncharged body is neutral.  Unlike Dufay, Franklin thought wrongly that there was only one type of electricity, and was using the terms positive and negative in the same way as we might use it when referring to money in a bank.

 Benjamin Franklin is probably more famous for flying kites in thunderstorms in his study of lightening.

 

 

Task 7

While working at the University of Leyden in the Netherlands, Mussenbroek discovered that electricity could be stored in a bottle!  The device came to be called the Leyden Jar.

 

Task 8

In  1748 William Watson transmitted discharge from a Leyden Jar along a circuit over 4km long and concludes wrongly that electrical impulses are instantaneous.

 

Task 9

Alessandro Volta invented the electrophorus.  It consisted of a metal plate with an insulating handle which sits on a charged insulator.  Using this device he was able to produce almost inexhaustible amounts of electrical charge. He wrote to Priestley to explain his discovery.

 

Task 10

Abraham Bennet invented a simple instrument for the detection and testing of small electric charges.  The gold-leaf electroscope consists of a small metal plate with a leaf of thin gold attached.  The leaf is protected from draughts by enclosing it in an earthed metal case with a glass window either side.

 

wpe8.gif (64258 bytes)Task 11

Joseph Priestley correctly suggested that the force caused by static electricity might follow a mathematical relationship called the ‘Inverse-square law’.

Using Priestley’s idea, Coulomb made quantitative measurements of the force of attraction and repulsion between charged objects.  The equation for this effect is now known as Coulomb's law and the unit of measurement of charge as the Coulomb.