Texto 4
When he was 19, in 1898, Albert Einstein was refused a place at the Munich Technical Institute because he 'showed no promise'. Three years later, Einstein took Swiss citizenship and became an examiner at the Swiss Patent Office. In his spare time, he continued his study of physics and by 1905 had advanced so far that he was able to publish the first of his celebrated papers on the theory of relativity which earned worldwide fame.
In: I wish I’d never said that, Oxford, Past Times, 2001, p. 60.
What's the meaning of the underlined word in the following sentence: “In his spare time, he continued his study of physics (...)”?