Sentence:  This and other fears of the solar system have <WSD>disappeared</WSD> gradually , first , with the Ptolemaic system and its built-in concept of periodicity and then , more firmly , with the Newtonian innovation of an universal force that could account quantitatively for both terrestrial and celestial motions . 
Meaning of the word marked with <WSD> tags:  get lost, as without warning or explanation