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Napoleon's defeat in the Battle of Waterloo was caused in part by electrically charged ash from an Indonesian volcanic eruption in 1815, according to new research.

The Duke of Wellington was assisted in defeating the forces of the French Empire by horrendous weather caused by the eruption, academics at Imperial College London have said.

Two months before the battle, a volcano named Mount Tambora erupted in Indonesia, killing 100,000 people and spraying so much ash into the atmosphere that the planet cooled and the following year was known as the "year without a summer".

While it is believed that the conditions on the battlefield contributed to the Allied army's defeat of the French Emperor, it wasn't apparent how electrified volcanic ash played a crucial role in shaping the direction of human history.

Dr Matthew Genge from Imperial College London discovered that ash from eruptions can "short-circuit" the electrical current of the ionosphere, the highest level of the atmosphere responsible for cloud formation.

Military strategists and even novelist Victor Hugo have suggested how the soaked grounds of Belgium on which the Battle of Waterloo was fought changed the course of history.

Dr Genge said: "Vigo Hugo in the novel Les Miserables said of the Battle of Waterloo 'an unseasonably clouded AG百家乐在线官网 sufficed to bring about the collapse of a world'.

"Now we are a step closer to understanding Tambora's part in the battle from half a world away," he explained.

Dr Genge's work has suggested that the eruption short-circuited the ionosphere, causing a pulse of cloud formation and heavy rains across Europe which led to Napoleon's defeat.

His paper showed that eruptions can hurl ash higher into the atmosphere than previously thought, up to 100km (62 miles) above ground - more than ten times higher than an average commercial flight.

Dr Genge said: "Previously, geologists thought that volcanic ash gets trapped in the lower atmosphere, because volcanic plumes rise buoyantly.

"My research, however, shows that ash can be shot into the upper atmosphere by electrical forces."

Weather records are rare for 1815, so Dr Genge examined those following the 1883 eruption of another Indonesian volcano, Krakatoa.

His data showed lower temperatures and reduced rainfall immediately after the eruption began, and that global rainfall was lower during the eruption than before or after.

He also examined reports of ionosphere disturbance after the 1991 eruption of Mount Pintatubo, which his models explain as being caused by the electrically charged ash in the ionosphere.

Dr Genge's findings are published in the journal Geology and could confirm a link between the "act of God" and Napoleon's famous defeat - ending the Napoleonic Wars which had ravaged Europe for 12 years.

His work was funded by the UK Science and Technology Facilities Council.