By MATTHEW KALMAN, Daily Mail

Last updated at 19:49 10 July 2006

Scientist Albert Einstein was a bad businessman, a prodigious lover with a string of mistresses and an absent father plagued by doubt about his relationship with his two sons.

This is the intimate picture which has emerged from a treasure trove of more than 3,500 pages of letters, postcards and other documents released publicly for the first time at the Hebrew University of Jerusalem.

They include notes and drawings to and from his children and his two wives, Mileva and Elsa. In one note to his son, Einstein drew a small cartoon of himself lying ill in bed, complete with a chamber pot at the ready.

Einstein bequeathed his personal papers to the Hebrew University when he died in 1955. The letters released however, were an additional bequest added to the collection by his step-daughter Margot Einstein on condition that they be sealed for 20 years after her death in July, 1986.

The letters reveal for the first time how the father of the theory of relativity lost most of his Nobel Prize money in bad stock investments on Wall Street, and provide details of how he was showered with affection and gifts by his mistresses.

He became involved with Elsa, a cousin, in 1912 when he was still married to his first wife Mileva, a fellow scientist with whom he had two boys, Hans Albert and Eduard. Before they married, they also had a daughter, Lieserl, who was given up for adoption.

Einstein divorced Mileva and married Elsa in 1919, but within four years he was already involved with Bette Neumann, his secretary who was also the niece of one of his friends. Many more liasons followed.

The letters reveal how one of his women, a beautiful Berlin socialite called Ethel Michanowski, followed him to Oxford, only to discover that he was involved with a another woman.

Einstein discussed his extra-marital affairs openly in letters to his daughter and his wife.

"It is true that M. followed me and her chasing after me is getting out of control," wrote Einstein to his step-daughter Margot in May 1931.

"I will tell her that she should vanish immediately. Out of all the dames I am in fact attached only to Mrs L. who is absolutely harmless and decent. I dont care what people are saying about me, but for mother and Mrs M. it is better that not every Tom, Dick and Harry gossip about it," he wrote.

'Mrs L.' was Margarete Lenbach, another wealthy woman who used to send a chauffeur-driven car to collect Einstein for their late-night trysts.

Einstein's distance from his two sons after the divorce from Mileva clearly troubled him. He writes how much he enjoys taking the boys on holiday but at times expresses despair at his younger son Eduard, who suffered from schizophrenia. On more than one occasion he suggests it would have been better if Eduard had never been born.

Extra-marital affairs

But things were troubled even before the split, not least because of Einstein's womanizing. In June 1915, Einstein went off on holiday with his cousin Elsa, who he would later marry, after his older son Hans Albert curtly rejected an invitation to join him.

"Dear Papa, You should contact Mama about such things, because I'm not the only one to decide here. But if you're so unfriendly to her, I don't want to go with you either," wrote his son, then just 11 years old.

The divorce settlement with Mileva contained a unique clause, in which Einstein agreed that should he win the Nobel Prize he would deposit the money in a Swiss bank account in Mileva's name and she could use the interest to finance the upbringing of the children. Einstein failed to fulfill this promise, and Mileva always felt betrayed.

The newly-released papers reveal that he invested

three-quarters of the money, some $24,000, in long-term bonds via the Ladenburg and Thalmann Bank in New York. Mileva was supposed to receive the interest. But the value of the bonds were wiped out in the American Depression of the 1930s

and Mileva's income dried up.

On 12 June 1932, Mileva asked her ex-husband for more money to help pay the mortage on properties she had bought. "Not much is left for us to live on, especially since our income in any case has been reduced because of the loss from the papers in America," she wrote.

But over the course of his life he sent Mileva and the boys regular sums of cash, much more than if he had only given them his Nobel Prize award.