Sentence:  Laplace (1749–1827) "saved the world" by using probability theory to estimate the parameters accurately enough to show that the drift of Jupiter was not <WSD>secular</WSD> after all; the observations at hand had covered only a fraction of a cycle of an oscillation with a period of about 880 years. 
Meaning of the word marked with <WSD> tags:  Relating to long-term non-periodic irregularities, especially in planetary motion or magnetic field.