1950-Thomas Kuhn wrote a book called The Structure of Scientific Revolutions, where he describes how science has developed, unlike any other book before it. Before this time there were few books that explained scientific change, theoretically. Prior to this, the philosophy of science during that time, sort of directed how science should develop. It was the opinion of certain philosophers, that science developed by building new truths on top of old truths. Kuhn was the first person to provide a written document which disagreed with the popular view. Kuhn believed that science, over time, was not uniform but when through different phases. Some of these phases were known as revolutions. Revolutionary periods were when an unexplained event occurred in the scientific pathway, that got you closer to solving a theory in science, even if it was previously assumed to be solved. These revolutions were seen as something positive and something to strive for. It made science better. At any time when scientists reached a point where they could not further their theories, or they reached a road block of some sort, it was referred to as a crisis. This was the prime time of when scientists searched for breakthroughs, and how science got better. I believe this is what Kuhn referred to as the revolutions.
Bird, Alexander. “Thomas Kuhn.” Stanford Encyclopedia of Philosophy, Stanford University, 13 Aug. 2004, plato.stanford.edu/entries/thomas-kuhn/#3.