A letter from Albert Einstein thanking a man from Chicago for helping Jews to escape Nazi Germany has been made public.

In 1939 the scientist wrote a series of notes thanking individuals for helping Jews during the Nazi period; until now historians had known about two but now a third has been revealed.

Einstein contacted to David Finck, a financier from New York, to "offer my sincere congratulations to you on the splendid work you have undertaken on behalf of the refugees". He had never met Mr Finck but was aware of his efforts to fund the emigration of Jewish refugees from Europe in 1939 before the outbreak of World War II.

Mr Finck's daughter, Enid Bronstein, told Chicago’s WGN TV that she had been keeping the letter in a safe deposit box since her father's death, but has now decided to share it. 

"I wanted to keep the letter to show it to my children and grandchildren so that they would get the message that every contribution, no matter how small, is important," she said.

Ms Bronstein says that while similar letters have sold for thousands of dollars at auction, she decided to donate it to the United States Holocaust Memorial Museum.

In the letter, Einstein, himself a Jewish refugee from Nazi Germany, wrote: “The power of resistance which has enabled the Jewish people to survive for thousands of years has been based to a large extent on traditions of mutual helpfulness. We have no other means of self-defence than our solidarity and our knowledge that the cause for which we are suffering is a momentous and sacred cause."