Conversation so far:
What was James Watt's first engine?
The first, for example, had a cylinder with a diameter of some 50 inches and an overall height of about 24 feet.
When did he make his first engine?
In 1776, the first engines were installed and working in commercial enterprises.
Did any other models follow that one?
Over the next six years, he made a number of other improvements and modifications to the steam engine.

Question: What modifications were made?
Self-contained rewrite: What modifications did James Watt make to the steam engine?