Great Scientists and their Inventions

Benjamin Franklin(Lived 1706 – 1790)

benjamin franklin

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Benjamin Franklin discovered one of the fundamental laws of physics – the Law of Conservation of Electric Charge – and proved that lightning is electricity. He also:

1. Invented bifocal spectacles

2. Invented the Franklin stove

3. Invented the lightning rod

Benjamin Franklin lived his life in the spirit of a renaissance man: he was deeply interested in the world around him, and he excelled in several widely differing fields of human endeavor.

He had a profound effect on our understanding of electricity and shaped the language we use when we talk about it, even today.

Here we shall concentrate on his life as a scientist and an inventor, only briefly touching on his other achievements.

Benjamin Franklin’s Science, Innovation, and Inventions

Franklin was an original thinker, scientist and inventor. Dating his inventions is not always easy, because Franklin did not patent what he invented. He said that anyone who wanted to make money from his ideas was free to do so. This means the dates given to his inventions are approximate.

Bifocal Spectacles

Franklin wore spectacles for most of his life.

He felt limited by the spectacles of his day, because a lens that was good for reading blurred his vision when he looked up. Working as a printer, this could be infuriating.

He defeated this problem in about 1739, aged 33, with his invention of split-lens bifocal spectacles. Each lens now had two focusing distances. Looking through the bottom part of the lens was good for reading, while looking through the upper part offered good vision at a greater distance.

The Franklin Stove

As Franklin read more about science, he learned more about heat transfer. He looked at the design of a typical stove and concluded that it was inefficient. Much more heat was lost up the flue than necessary.

He decided to redesign the stove using the concept of heat-exchange/heat recovery.

The idea was that hot gases which would normally simply go up the flue would exchange their heat with cold air from the room, heating it up, and so heating the room up.

In 1741, the Franklin Stove came on to the market, allowing homeowners to get more heat into their homes for each unit of fuel they burned.

The Lightning Rod

Even today, we still use Benjamin Franklin’s lightning rod.

Like his other ideas, he did not patent it: he profited from the lightning rod intellectually, not financially.

Since the time he invented it, it has saved societies all over the world great amounts of time and money by protecting buildings from damage. It has also, of course, saved countless lives.


In 1758, working with John Hadley in Cambridge, England, Franklin investigated the principle of refrigeration by evaporation.

In a room at 18 °C (65 °F) , the scientists repeatedly wetted a thermometer with ether, then used bellows to quickly evaporate the ether.

They were finally able to achieve a temperature reading on the thermometer of -14 °C (7 °F).

We now know the reason for the refrigeration effect. We have learned that molecules in a liquid have a range of energies. Some have high energy, and some have low energy. Molecules carrying the most energy escape from the liquid most easily – they evaporate. This leaves the lower energy, colder molecules in the liquid. The result is that the temperature of the liquid falls.


By observation of storms and winds, Franklin discovered that storms do not always travel in the direction of the prevailing wind. This was an important discovery in the development of the scientific discipline of meteorology.


Benjamin Franklin died on April 17, 1790, at the age of 84. He was killed by pleurisy – a lung inflammation.


They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.

An investment in knowledge pays the best interest.

Early to bed and early to rise makes a man healthy, wealthy, and wise.