- [Man] As we enjoy great advantages
from the invention of others,
we should be glad of an opportunity to serve others,
by an invention of ours.
And this, we should do freely, and generously.
- [Narrator] But nothing he did as a scientist would
do more to serve others and bring him more fame
than his work in the fledgling field of electricity.
"I never was before engaged in any study," Franklin wrote,
"that so totally engrossed my attention and my time."
- [Clay] Franklin had become interested in electricity,
which at the time was certainly not understood,
but it was also a sort of a parlor trick.
People would come in with a glass rod and some silk,
and shock each other and lift pieces of paper.
- [Narrator] He and his Junto friends staged
electricity parties,
in which they used a charge to ring bells,
and make a toy he called an Electrical Spider jump around.
Men and women exchanged electrical kisses.
Franklin also electrified a gilt edged portrait
of King George the Second.
That created what he called a high treason shock,
if someone touched his crown.
He used a more powerful shock to kill a turkey,
and reported that it seemed uncommonly tender
compared to one slaughtered the conventional way.
- [Walter] He kept saying we have to find useful things
to do with this electricity,
he said one of the only useful things
in his first year of experiments
was that he would get shocked and knock him down,
and he said electricity was useful for making
a vain person humble.
- [Narrator] As his studies turned more serious,
and he began documenting his observations,
he came up with new terms
to describe electricity's mysterious properties.
"It had two charges," he wrote, "positive and negative."
And it could travel, by what he called a conductor.
He grouped a collection of glass containers together,
each possessing an electrical charge,
and named it a battery,
using the military term for an array of cannons.
- [Walter] Benjamin Franklin comes up with the most
important theory of the era,
which is the single fluid theory of electricity.
Which is, that it's not some substance,
but it's a positive and a negative,
and it flows from positive to negative.
- [Narrator] But pure science had less appeal to Franklin
than putting it to practical use.
- [Philip] Lightning is seen as being divine retribution,
of course the irony was that most of the buildings
that were destroyed by lighting were churches,
'cause in a lot of communities in the 18th century,
they were the highest structure.
- [Walter] Franklin is convinced that lightning bears
a similarity to an electrical spark.
He's looking at electric sparks,
he's looking at lightning,
and he puts in his notebook all the similarities.
And at the end of the page,
he says "let the experiment be made."
- [Narrator] Franklin detailed his theory
that lightning was electricity,
and that metal objects could draw off a charge.
He proposed an experiment that involved placing a person
in what he called a sentry box, on a high tower or hilltop,
and raising a sharply pointed iron rod
when storm clouds approached.
He shared his observations with
a London scientist, Peter Collinson,
who had supplied him with equipment
for his electrical studies.
Franklin was planning to conduct the experiment on
the new steeple of Christ Church off Market Street,
as soon as its construction was completed.
But the work went slowly, and Franklin grew impatient.
He then came up with an alternative way to test his theory.
He was less confident in this method,
and decided to do it in secret,
trusting only his son William to take part.
In June of 1752, with storm clouds threatening,
he and William went to a field with a silk kite,
to which Franklin had attached a sharp pointed wire.
Dangling at the end of the kite's long twine string
was a metal key.
They got the kite aloft,
and Franklin maneuvered it toward the approaching clouds.
- [Philip] What he was showing was that
the atmosphere became electrified.
Not that the kite had to be struck by a lightening bolt,
which is often the way that it's depicted in illustrations.
- [Narrator] Franklin suddenly noticed the individual
strands of hemp along the kite's string stiffening,
and standing on end.
He moved his free hand toward the key,
and felt a mild shock on his knuckle.
When the rain began,
and water started streaming down the twine,
sparks flew off the key.
Franklin was exultant.
"Thereby," he wrote of his experiment,
"the sameness of electrical matter with
that of lightening has been completely demonstrated."
- Hi, this is Ken Burns.
I hope you enjoyed that excerpt from the film David Schmidt
and I made exploring the extraordinary life
of Benjamin Franklin.
Here are some more clips you might like
and you can watch the entire "Benjamin Franklin" series
on the PBS Video App or at pbs.org.