A substantiated opinion because Reagan quotes an expert.
Explanation:
In the excerpt , Reagan is expressing a substantiated opinion because he is quoting an expert, the expert being Mikhail Lomonosov, a Russian scientist and writer from the seventeenth century.
Reagan is quoting Lomonosov in order to add authority to his speech, so that his speech does not only express his own views, but also the views of a renowned person who had similar ideas.
The purpose of these lines is to show that every beautiful thing some time will lose its beauty either by time (nature's changing course) or by chance e.g. an unfortunate event
