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Benjamin Franklin: Science Years
(Ages 40 - 49)

by Ron Kurtus (revised 19 January 2022)

From the age of 12 to 39, Benjamin Franklin worked in the publisher business in Philadelphia. He then retired from publishing and turned to scientific studies.

His inventions and experiments in science soon brought him world-wide fame. His most notible experiments were with electricity.

Questions you may have include:

This lesson will answer those questions.

Ages 40 to 46 (1746 - 1752)

At age 42, Franklin retired from the printing profession. He then devoted his time to other studies, especially science. These were very productive years in his life, bringing him world-wide fame as a scientific thinker.

Interested in electricity

Franklin was ever curious and inquisitive. He became interested in electricity after seeing demonstrations about static charges and the Leyden Jar. Afterwards, he used a method of rubbing glass tubes with silk to generate the static electric charges that could be used in many of his experiments.

Invented lightning rod

Franklin felt that lightning was electricity that came from the clouds. To prove this theory, he set up tall, pointed metal rods to provided a path for the electricity of lightning to follow. His experiments in attracting lightning to the rods resulted in the invention of the lightning rod, designed to protect people's dwellings.

Because of the invention, Franklin received accolades. But he remained modest and even refused to patent the lightning rod or attempt to profit from it.

Performed kite experiment

To continue his study of the relationship of lightning and electricity, the 46 year old Franklin devised his famous kite experiment with the aid of his 21 year old son, William.

One day, during a thunderstorm, he flew a kite in the storm. Little did he know that this was a very dangerous thing to do.

Franklin flying kite with his son

Franklin flying kite with his son

(Note: Either 21 year old William was very small for his age, or the artist goofed)

He had attached a metal key to the end of the kite string. As the rain fell and the wind blew, he noticed the hairs on the kite string stand on end, just as they would do if you combed your hair and put the comb near the string. He was able to make a spark jump from the key to his finger.

Luckily, he ended his experiment then, because he easily could have been electrocuted from his experiment. Franklin seemed only dimly aware of the experiment's potential danger.

Invented lightning bells

Also at age 46, Franklin developed another device to help him understand electricity, called lightning bells. These bells would jingle when lightning was in the air.

Did another risky experiment

To make these lightning bells work, Franklin used the lightning rod he had erected on his roof and ran a wire from it into his house. He divided the wire into two wires, which were attached to two small bells separated by 6 inches.

Between the bells was a little brass ball, suspended by a silk thread. When storm clouds passed with electricity in them, the ball would go back and forth, ringing the bells.

Franklin was fortunate to disconnect his experiment before a lightning bolt struck the rod and set his house on fire.

Lucky not killed

Although his scientific curiosity moved him toward inventive experiments, he was lucky he was never killed with these dangerous experiments. Once he received such a severe electrical shock that his body actually went into seizures. He was more careful after that.

Became famous

Franklin's electrical experiments brought him instant fame, and crowds began to gather around his home, hoping to catch a glimpse of the "wizard of electricity."

Started fire insurance

In his 46th year, he also was responsible for setting up America's first fire insurance company.

The year 1752 certainly was an active time in his life.

Ages 47 to 49 (1753 - 1755)

The next several years Franklin continued his scientific studies, as well as creating useful inventions.

Coined electrical terms

Franklin coined many of the electrical terms we use today, such as battery, conductor, condenser, positive and negative charge, electric shock and electrician.

Had several inventions

Franklin studied other scientific areas than electricity. He invented the catheter, bifocals, and the Franklin stove, among other things.


Ben examined medicine and invented the medical instrument known as a catheter in order to treat his ill brother. He also formulated theories about the circulation of blood in humans.


Franklin wore glasses, and after the age of 40 he needed another pair for reading. To solve that problem, he split the lenses of each pair of glasses, such that the top half was for distances and the bottom half was for reading. In this way, he would not have to constantly change his glasses. This was the invention of the bifocal glasses.

Franklin Stove

Franklin was always noticing problems or irritations and trying to solve them. For example, when he noticed the problem of heating houses, Franklin invented a type of stove that would do the job more effectively. This was called the Franklin Stove.

Background of his genius

What made his achievements during these years even more remarkable was the fact that Franklin had no formal education in the sciences. He relied purely on his powers of observation, his personal intellect and curiosity.

Since he was an amicable person with a good sense of humor, he had many friends—including those who specialized in science. From letters and conversations with these scientists, Franklin gained insight and ideas for his experiments.

Also, part of Franklin's genius was that he sought to master every endeavor that he put his mind to, from printing to science to politics.


During the years in his 40s, Benjamin Franklin gained fame through his experiments in electricity. He also came up with a number of inventions during this time of scientific study. He was inquisitive and observant, leading to his discoveries. In the later years of his life, he spent more time on statesmanship, representing his country in Europe.

Learn by experimenting

Resources and references

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Benjamin Franklin: Science Years (Ages 40 - 49)

Publishing Years (Birth to Age 39)

Statesman Years (Ages 50 - 84)

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