This June, 1954, file photo shows renowned physicist Albert Einstein in Princeton, N.J. Einstein was a father who worried his son wasn't taking his geometry studies seriously enough, and that he was indebted to a favorite uncle for giving him a toy steam engine when he was a boy, launching a lifelong interest in science. He also believed the infidelity of a friend's spouse was no big deal. These and other reflections, including personal opinions on God and politics, are contained in 27 letters being offered by a private collector at auction this week. (AP Photo, File)

When he wasn't busy scribbling out the theory of relativity, Albert Einstein seems to have spent a fair amount of time writing letters involving topics such as God, his son's geometry studies, even a little toy steam engine an uncle gave him when he was a boy.

The Einstein Letters, which include more than two dozen missives, will go up for sale Thursday at the California-based auction house Profiles in History. Some were in English and others in German. Some were done in longhand, others on typewriters.

Amassed over decades by a private collector, the letters represent one of the largest caches of Einstein's personal writings ever offered for sale.

But more than that, they give a rare look into Einstein's thoughts when he wasn't discussing complicated scientific theories with his peers, said Joseph Maddalena, founder of Profiles in History.

"We all know about what he accomplished, how he changed the world with the theory of relativity," Maddalena said. "But these letters show the other side of the story. How he advised his children, how he believed in God."

In one letter, Einstein urged one of his sons to get more serious about geometry. In another, he consoled a friend who recently discovered her husband's infidelity. In still another to an uncle on his 70th birthday, Einstein recalled how the toy steam engine the uncle gave him years ago had prompted a lifelong interest in science.

On the issue of God, Einstein dismissed the widely held belief that he was an atheist.

"I have repeatedly said that in my opinion the idea of a personal God is a childlike one," he wrote to a man who corresponded with him on the subject twice in the 1940s. "You may call me an agnostic, but I do not share the crusading spirit of the professional atheist. ... I prefer an attitude of humility corresponding to the weakness of our intellectual understanding of nature and of our own being."

This undated image provided by Profiles in History shows a letter written on September 28, 1949, by legendary physicist Albert Einstein on his idea of God. He's known far and wide for the theory of relativity, for research that helped lead to the development of the atomic bomb and as the most brilliant physicist of the 20th century. Lesser known is that Albert Einstein was also a father who worried his son wasn't taking his geometry studies seriously enough, that he was indebted to a favorite uncle for giving him a toy steam engine when he was a boy that launched a lifelong interest in science. He also believed the infidelity of a friend's spouse was no big deal. These reflections and other personal opinions on God and politics are contained in 27 letters being offered by a private collector at auction this week. (Profiles In History via AP)

Maddalena expects the 27 letters to fetch anywhere from $5,000 to as much as $40,000, for a total take ranging from $500,000 to $1 million. They are priceless, in his opinion, when it comes to having a greater understanding of the most brilliant physicist of the 20th century, the man whose theories ushered in the atomic age.

"These are certainly among the most important things I've ever handled," Maddalena said. "This is not like a Babe Ruth autograph or a signed photo of Marilyn Monroe. These are historically significant."

This undated image provided by Profiles in History shows a letter written by legendary physicist Albert Einstein about his theory on relativity. Einstein was a father who worried his son wasn't taking his geometry studies seriously enough, and that he was indebted to a favorite uncle for giving him a toy steam engine when he was a boy, launching a lifelong interest in science. He also believed the infidelity of a friend's spouse was no big deal. These and other reflections, including personal opinions on God and politics, are contained in 27 letters being offered by a private collector at auction this week.(Profiles In History via AP)

This undated file photo shows legendary physicist Dr. Albert Einstein, author of the theory of Relativity. Einstein was a father who worried his son wasn't taking his geometry studies seriously enough, and that he was indebted to a favorite uncle for giving him a toy steam engine when he was a boy, launching a lifelong interest in science. He also believed the infidelity of a friend's spouse was no big deal. These and other reflections, including personal opinions on God and politics, are contained in 27 letters being offered by a private collector at auction this week. (AP Photo/File)

Explore further Einstein letter on God to be auctioned on eBay

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