"The general concept from everything we knew before was that he was a poor father, that he did not meet his responsibility to his children and that he was quite cruel to his wife," Professor Gutfreund said. "From the documents we have now, a different picture emerges. He does show empathy and compassion."

There is evidence that Einstein diverted part of his money from the Nobel Prize into providing for Mileva and his children. He invested the rest, and lost much of it in the Great Depression.

Einstein's schizophrenic son, Eduard, is also mentioned in the new letters. "He refers [in previously known letters] to Eduard as maybe it would have been better if he would not have been born," said Professor Gutfreund. But in the new letters Einstein mentions his pleasure in receiving poems, pictures and notes from Eduard. Einstein wrote: "The more refined of my sons, the one I considered really of my own nature, was seized by an incurable mental illness."

He also writes of his weariness at being associated with his theories. "Soon I'll be fed up with the relativity," he wrote to Elsa. "Even such a thing fades away when one is too involved with it."

SMT

The 3,500 hand-written pages include letters sent by Einstein to his second wife, Elsa, and others received from his sons and two wives, Barbara Wolff of Jerusalem's Hebrew University's Einstein Archives told AFP.

The letters, Wolff said, were willed by Einstein to his stepdaughter, Margot, and were kept sealed for 20 years after her death to protect the privacy of the individuals mentioned.

"Through the letters, we received information on the other side of Albert Einstein," said Wolff, who has read all of the letters over the past two years.

"We can see a much more human image than the sterile person presented 30 years ago in biographies," based mostly on Einstein's secretary in the 1950s, "who presented him as a genius with no personal or sex life".

Wolff said nevertheless that the newly released material shed no new light on Einstein's science , but that "if the image we had of Einstein before had three colours, now it has six."

Einstein and his first wife, Mileva, had two sons together. After their divorce he married Elsa, a cousin.

Previous biographies presented him as cold and cruel toward Mileva, but the letters now reveal that "his relations with his children and wives were filled with much more love and affection", Wolff said.

"I dreamt that Margot had married as well. I love her as much as if she were my own daughter, perhaps even more, since who knows what kind of brat she would have become (had I fathered her)," Einstein wrote to Elsa in 1924.

But the letters also reveal Einstein openly discussed with Elsa and Margot his numerous love affairs.

"It is true that M. (Ethel Michanowski, a Berlin socialite who was involved with Einstein in the late 1920s and early 1930s) followed me (to England), and her chasing after me is getting out of control," he wrote to Margot in 1931.

"But firstly I could hardly avoid it, and secondly, when I see her again, I will tell her that she should vanish immediately ... I don't 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."

In a letter dated from 1921, just one year after the experimental confirmation of Einstein' prediction of the bending of light, or relativity theory, he says "soon I'll be fed up with the relativity".

"Even such a thing fades away when one is too involved with it," wrote the German-born Einstein who died in 1955 at the age of 76.