"Kissinger's on his way back and we got the agreement," he told her. "I'm going to announce it at 10 tonight on television."
"Oh, great. Isn't that marvelous. It's wonderful," his wife replied.
In one letter, he states his firm support for the Equal Rights Amendment. For 20 years, he says in the letter, "I have not altered my belief that equal rights for women warrant a constitutional guarantee."
Despite his support, the amendment failed.
But that support for women's rights is in odd juxtaposition to what he says in a taped conversation with George H.W. Bush, who was the GOP chairman at the time.
In the recorded conversation, Nixon pushed for the party to recruit pretty women to run for office, after two women caught his eye in the South Carolina Legislature.
"Let's look for some," he said. "And understand, I don't do it because I'm for women. But I'm doing it because (a) woman might win some place where a man might not."
Other issues that the tapes document are the return of American prisoners of war from Southeast Asia, efforts to maintain U.S. access to oil in the Middle East, and the Supreme Court's decision to legalize abortion with the Roe v. Wade ruling.
More than 2,200 hours of secretly taped conversations from Nixon's presidency have been released since 1980, and there are still more to come.
The Associated Press contributed to this report.