Dressed in academic regalia in a convocation ceremony in the quad, Hennessy urged them to emulate Benjamin Franklin's qualities of intellectual curiosity and passion for learning.
"Indeed, Franklin's entire life was an intellectual journey, just as we hope the next few years of your lives will be," he told 1,709 freshmen and four dozen transfer students, who took up residence on campus Tuesday.
The new students come from all 50 states and from 52 countries. The 1,709 freshmen are the ones who said "yes" to Stanford out of the 2,427 students admitted from an initial applicant pool of 34,348.
Thirty-nine percent of Stanford's class of 2015 graduated from high schools in California, and 16 percent of the freshmen are the first in their families to attend a four-year college. Nearly half receive financial aid from the university.
Caucasians comprise 30.6 percent of the class; Asian-Americans 22.4 percent; Hispanics 15.4 percent; African-American students 10.6 percent; Native-Americans and Hawaiians 4.7 percent, with the remainder unknown, the university said.
A quarter of the entering class members said they are primarily interested in natural sciences, followed by engineering (21 percent); pre-law and pre-medicine (18 percent); humanities (17 percent); social sciences (12 percent); earth sciences (2 percent) and "undecided" (5 percent).
Ninety-two percent of the Class of 2015 ranked in the top 10 percent of their high school graduating classes, and 87.5 percent earned high school GPAs of 3.8 or higher.
Among 47 transfer students who also arrived Tuesday, 21 graduated from community colleges and nine are U.S. military veterans.
A 44-page "major events" calendar for new students began with the welcome from Hennessy Tuesday afternoon. The week has been packed with placement testing, library tours, advisor meetings, faculty research presentations, religious services, cultural group welcomes and parties.
On Thursday, new students were invited to a "first lecture" by celebrated author and Medical School Professor Abraham Verghese. The topic was "the purpose of a liberal education and how you will become more than your major."
Orientation wraps up Sunday with a discussion moderated by Political Science Professor Scott Sagan with the authors of three books freshmen were assigned to read over the summer: "March" by Geraldine Brooks; "The Violence of Peace" by Stephen L. Carter and "One Bullet Away" by Nathaniel Fick.
Sagan said he chose the books because he wants students to understand current global conflicts and ethical issues in war.
"I think war is too important for young people at a major university to ignore," he has said.
In a June letter to freshmen, Sagan said, "Students at an American university should not forget that the United States is currently engaged in wars in Iraq, Afghanistan and Libya, and 15 additional civil wars are raging elsewhere, and that U.S. troops are deployed in many U.N. peacekeeping missions.
"Our peaceful intellectual oasis exists in a world of conflict."
Noting that reasonable people often disagree, Sagan said he wants students "to wrestle with the ethical dilemmas involved in decisions about war and peace."
In Tuesday's welcoming ceremony, Hennessy told an apocryphal story about a conversation Benjamin Franklin had in a Philadelphia tavern with a man who said the words in the Declaration of Independence "don't mean nothing at all."
The man asked, "Where's all that happiness the document says it guarantees us?"
Franklin was said to have replied, sympathetically: "My friend, the Declaration of Independence only guarantees the American people the right to pursue happiness. You have to catch it yourself."
"And so it is with your time here at Stanford," Hennessy told the freshmen. "You will have many opportunities here but it is incumbent on each of our students to catch them."
Regular classes for Stanford undergraduates begin on Monday.