A 23-year-old physics student has discovered an error in Sir Isaac Newton's ''Principia'' that had gone undetected since the work laid out the laws of motion and gravity 300 years ago.
''It's great that I found it, but it certainly doesn't change history's view of Newton or anything,'' said the student Robert Garisto, who is a senior at the University of Chicago. ''What I found is that Newton, using his own data, plugged the wrong value into a calculation.''
The equation in question appears in Proposition Eight of Book Three of the ''Philosophiae Naturalis Principia Mathematica,'' one of the greatest works in the history of science.
The Principia, published in 1687, argued that a unified system of scientific principles governed what happened on Earth and in the heavens.
In Proposition Eight, Newton tried to demonstrate the correctness of his explanation by calculating the mass, surface gravity and density of the known planets. To determine the mass, he needed to know the angle between a line from the center of the Earth to the Sun, and a line from a point on Earth to the Sun. Routine Class Assignment
Modern science has put that number at about 8.8 seconds. (A second is one-3,600th of a degree.) Newton believed the figure to be 10.5 seconds, but he mysteriously used 11 seconds in the equation. That is the error Mr. Garisto discovered when he repeated those calculations as part of a routine class assignment.
''When I found the discrepancy, my initial reaction was 'Wow!' '' he said. But he simply turned in the assignment, assuming students were expected to find the discrepancy. That was mid-February. But the significance of the find eluded even Prof. Noel Swerdlow, who gave Mr. Garisto an A-plus for his paper. He had made the assignment because he had never been able to get the numbers in Proposition Eight to agree with each other.
In April, Professor Swerdlow and Mr. Garisto attended a lecture on the ''Principia'' by Prof. Subrahmanyan Chandrasekhar, a univeristy astrophysicist who is a Nobel laureate. Immediately afterward, Mr. Garisto and his teacher realized what the student had uncovered.
Mr. Garisto wrote a more extensive paper, submitted it to the scientific honor society Sigma Xi and won the university chapter's Prize for Excellence in Science, no small feat in a physics department that has 18 Nobel Prize winners among past or current students and faculty.
Mr. Garisto will receive a bachelor's degree in physics Saturday, and begin graduate work next fall at the University of Michigan, where he plans to continue his studies in theoretical high-energy physics and Einstein's theory of general relativity.
Asked whether he expected to find problems with Einstein's work, he laughed and said, ''Give me a break.''
