Electrostatic telegraphs (case study) Long before the internet people thought about sending information along wires using static electricity.
Electrostatic telegraphs (case study)
- Around 600 BC lived Thales of Miletus,
- widely regarded as the first Greek philosopher,
- as he was the first to give a purely natural explanation
- of the phenomena he observed.
- A key observation he made was that certain stones –
- such as amber – when rubbed against fur,
- would exhibit a strange property.
- The amber seemed to emit an invisible force
- which would attract small fibers.
- He assumed this rendered the amber magnetic,
- a [property] he observed when playing with lodestones,
- which are naturally occurring magnets.
- Many after him observed that contact or friction
- with fur seemed to create an imbalance.
- Something was pulled from the fur
- and transferred onto other objects.
- Now, not only did this result in a small
- attractive or repulsive force,
- but also in the potential for shocks to occur.
- Once the discharge occurred,
- the force disappeared.
- So the shock was some form of discharge
- which reversed the imbalance created by the friction.
- Throughout history,
- we were also fascinated with lighting bolts –
- nature's most passionate displays
- of power and aggression.
- Most cultures assumed this was a divine force,
- outside the reach of human hands,
- and was therefore reserved for the gods.
- Up until the 17th century, our descriptions of it
- varied from an invisible, intangible, imponderable agent –
- or even threads of syrup which elongate and contract.
- And it was Benjamin Franklin who, in 1752,
- set out to prove that there was a connection
- between lightning and these tiny shocks due to friction
- In a famously dangerous experiment –
- done alone with his son –
- he led a kite into a thunderstorm.
- And near the the bottom,
- where the thread was wet, he tied an iron key.
- And after some time,
- he brought his knuckle up to the key,
- and experienced a series of small shocks --
- identical to the ones created by contact with fur.
- This showed that, indeed,
- lightning was simply the same thing
- as these household shocks – but on a massive scale.
- And at this time, people had begun
- to divide materials into two categories.
- One [category included] objects which
- would allow or accept discharge – such as gold or copper –
- which we call 'electrical conductors.'
- And interestingly, these materials are also
- generally good at conducting heat.
- [In category] number two were objects
- which would not allow this discharge –
- such as rubber – [which we call] electrical 'insulators.'
- These materials also seem to
- insulate [against] the transfer of heat.
- And we also began trying to measure this force
- that Thales had encountered.
- One way to do this
- was to suspend a piece of spongy plant,
- called a pith ball, [by] a thread.
- And when we rubbed an insulator against fur,
- and brought it near the pith ball,
- [the insulator]would [appear to] pull on [the ball],
- causing a deflection [from the ball's normal resting position].
- If we added more objects,
- we noticed [that] this deflection increased --
- due to a greater pulling force.
- We also noticed that the shape of insulators
- made a difference.
- Large, thin insulators seemed to
- exhibit a much stronger force.
- And amazingly, it was found that conductors –
- such as copper wire –
- would transmit this pulling effect over a distance.
- This was demonstrated by running a long wire
- between the pith ball and the charged insulator.
- When the [charged] object was brought near the wire,
- [the charge] pulled through the wire –
- and deflected the pith ball instantly.
- When we later touch the wire with our finger,
- a discharge occurs, and the pulling stops,
- and the ball is released.
- Immediately, people began speculating
- that this could be the future
- of optical [or visual] telegraphs.
- And in 1774, French inventor, George-Louis Le Sage,
- was one of the first on record to actually set up this idea.
- He sent messages through an array of 26 wires –
- each wire representing a letter of the alphabet.
- When a discharge occurred at one end,
- the pith ball would move at the other.
- The trouble with this telegraph
- was that it only extended between
- the two rooms of his house.
- The power of the deflection was small
- and difficult to work with.
- Though at the time, people were investigating
- techniques for generating larger charge differences,
- in order to amplify the force involved.
- One improvement,
- popularized by Alessandro Volta one year later,
- was an easy way of generating discharges on demand.
- It was based on the idea that a charged insulator
- could induce or transfer a charge
- onto a nearby conducting plate.
- One needed to merely bring the metal plate
- close to the insulator, which would pull
- on the charge distribution in the metal plate,
- resulting in an imbalance – or electrical 'tension' –
- in the metal plate.
- Then one could bring their finger to the plate,
- and a discharge would occur.
- Then the plate is pulled away, using an insulating handle,
- and an excess charge would remain trapped in the plate.
- The plate could then be discharged at will,
- simply by touching it to a conductor – such as a finger.
- And amazingly, this process can be repeated many times
- without recharging the insulating plate.
- We could then generate many small discharges at will.
- And by now, Benjamin Franklin
- was focused on finding out how to trap –
- or store up – these discharges.
- At this time, he still assumed that
- electricity was some sort of invisible fluid –
- since he knew it could travel through water.
- So he assumed that water, inside an insulator,
- could hold electricity.
- What we now call the 'Leyden jar' was
- a glass jar with water inside,
- and a metal probe running out the top.
- Franklin also wrapped the outside in a conductive metal.
- When he brought a charged conductor
- towards the top probe, a discharge would occur,
- and stay trapped in the jar.
- More importantly, was that the jar could be charged
- multiple times.
- Each spark would amplify the charge separation –
- or electrical tension – inside the jar.
- A good analogy is to think of the jar as a balloon,
- and each discharge as a short jolt of water.
- And after hundreds of iterations,
- the tension becomes massive.
- And to release the charge,
- he simply touched the outside conductor to the top probe.
- A large discharge occurred.
- Franklin improved the design over time,
- eventually realizing that the charge was not
- stored in the water – but the glass.
- The water was merely a conductive path
- from the probe to the jar.
- Today, we would call the Leyden jar a 'capacitor' -
- or 'charge-storing device.'
- And when he chained many jars together,
- he found he could increase the capacity even more –
- and release deadly bolts of electricity.
- And over the years, people focused on
- more effective ways of building up charge –
- using friction machines –
- which could then be stored in capacitors
- and released as spectacular displays
- of man-made lightning.
- And over the next 50 years,
- people tried to design systems
- for sending sparks across greater distances,
- using longer wires, and more powerful discharges.
- However, sending electrostatic discharges –
- as a communication method –
- seemed clumsy, archaic, and was no improvement
- over the existing optical telegraphs of the day.
- They were widely ignored by government and industry.
- Though the tides were rising.
- An electric revolution was just around the corner.
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