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Furthermore, he discovered the long in-
equality of Jupiter and Saturn, whose pe-
riod is 929 years. For an investigation of
this also the Academy of Sciences offered
their prize. This led Euler to write a valu-
able essay disclosing a new method of com-
puting perturbations, called the instanta-
neous ellipse with variable elements. The
method was much developed by Lagrange.
291