Introduction

The machine

The story

Static history

The challenge

For teachers

For reference

 

Priestley's Story.

PriestleyPicture.jpg (37397 bytes)Joseph Priestley was born on March 13, 1733 in Yorkshire, England.  He studied to become a clergyman and in 1758 started to preach in a church in Cheshire. He also started a small school, for which he purchased scientific equipment, teaching pupils how to use it.

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He encouraged pupils to give science demonstrations to a live audience.  He introduced the ideas of using timelines in history and wrote his own textbooks.   He believed in freedom in education and encouraged students to question and advance their own ideas. This was all pretty radical stuff for the day!

Priestley became interested in gases whilst living next to a brewery in Leeds.  He was intrigued by the gas that floated over the fermentation vats.  He was the first to discover carbon dioxide, show that it extinguished a lighted splint of wood and that it was more dense than air.

  

He devised a method for making the gas and showed that it dissolved in water.  His  book 'On Making Carbonated Water' was printed in 1772.

He discovered that this bubbly water had a really pleasant taste and received a medal from the Royal Society for his work.  (The big bucks were to be made sometime later by Cola manufacturers!)

In 1772 Priestley was also the first to observe respiration in plants.  (The fact that they take in oxygen and give out CO2 ). This is best observed in the dark when it is not masked by the reverse process of photosynthesis.  And he discovered photosynthesis as well.  (The production of oxygen by a plant when in the light.) 

He needed to discover how to produce oxygen first of all and identify its properties. He left others to name these gases and explain more fully the chemistry behind the chemical reactions, but his achievements are quite impressive.  Aren't they?

Oh, and just for a giggle he discovered Nitrous Oxide (laughing gas).  Now that was a riot!  The serious application of using it as an anaesthetic was developed later.

So what's this to do with Physics? 

Quite by chance in 1766 he met Benjamin Franklin, who was one of the most prominent scientists of the day.  He is best remembered now for experiments involving flying kites in thunderstorms.  Don't try this one at home -  a Russian scientist tried to copy Benjamin, only to prove that electricity, water and ignorance is a deadly cocktail.

 

Joseph and Benjamin hit it off and became life long friends. Joseph became interested in Benjamin's special interest electricity. And he threw himself into this new area of study with gusto.

In 1767, just one year after meeting Franklin, Priestley had made his first electrical discovery that graphite can conduct electricity. Priestley's greatest contribution to physics was made later that same year. To explain it we need to go back one hundred years.

Sir Isaac Newton, had shown that the same force that pulls an apple to the ground is responsible for holding the Moon in orbit around the Earth. He even wrote mathematical equations that describe these forces.

Priestley suggested an analogy between gravity and electricity. According to Newton, inside a hollow sphere there is no gravitational attraction. Experimentally Priestley found that inside an electrified conducting sphere there was also no electrical attraction. He suggested that electrical interactions might follow the same form of equation as gravity. The first effective verification of Priestley's idea was made by the French engineer Charles Augustus Coulomb.

Newton's Law of Universal Gravitation is a very important equation. It helps to explain how the planets are kept in orbit.

Coulomb's Law  describes electrostatic force. This force is just as important to understand as gravity as it is the force that keeps molecules together. If it was not for electrostatic force, we and everything around us would disintegrate into a cloud of gas.

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Priestley suggested that electrostatic forces might follow very similar rules to those that hold the solar system together.
If we compare the two equations below we can see how remarkably similar they are:

You may not understand how to use these equations at the moment, but the two important points to be gained are:

1) They are pretty simple

2) They are remarkably alike.

 

Newton once explained to a fellow scientist how he had achieved so much, by saying that he could see so far by standing on the shoulders of others.
Priestley was very much of the same opinion. Many of his scientific books are careful to describe past achievements of others before explaining his own ideas. He was very much into the idea of collaboration between scientists. We know he kept in contact with Franklin and that Volta wrote to him to explain his newly discovered electrophorus. 

 

Priestly regularly met up with a group of influential scientists and industrialists called ' The Lunar Society'. They met by the light of the full moon, so that they could find their way home in the days before street lighting. (These scientists were no fools!)

It really was an amazing group of  individuals. 

It included Matthew Boulton the business partner of James Watt, the industrialist Josiah Wedgwood ,the astronomer William Herschel, John Smeaton, Erasmus Darwin (scientist and grandfather of Charles Darwin), and William Withering. The purpose of the group was to meet and discuss how the new sciences and technologies could best be used to better society and mankind.

 

So, Priestley was a mild mannered clergyman, successful scientist and popular with everyone.

 Wrong !

 Priestley was building up a list of enemies. You see he was passionate about changing society and scientific developments were part of the change which he knew was going to upset people. He once wrote:

'...the English hierarchy, has reason to tremble even at an air pump, or an electrical machine.'

In his religious teachings he fell foul of the orthodox church (a powerful body in those days). Worse still Priestley got involved in radical politics of the day and was a supporter of both the French Revolution and the struggle for independence in the American colonies.

Anti-American and anti-French feeling reached fever Pitch in July 1791 when an angry mob went on a rampage of destruction in Birmingham. It is usually referred to as the Birmingham riots, but there is a hint of conspiracy theory here as careful study of the evidence has convinced many historians that the events were more carefully organised than would be true of drunken rioters. All the victims of the violence and destruction were members of dissenting religious groups and supporters of the French Revolution. Priestley's house, library, his church and all his scientific apparatus were destroyed. He fled for his life to London, and two years later moved to the more welcoming America.

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