What significant contribution did William Harvey make to science?

William Harvey's significant contribution to science was his discovery of the circulation of blood. In the early 17th century, Harvey conducted extensive studies and experiments that led him to understand how blood circulates through the body. He demonstrated that blood is pumped by the heart and travels through a closed vascular system, effectively challenging the previously held views about the heart and blood flow. His work laid the foundation for modern physiology and our understanding of the cardiovascular system. This discovery was revolutionary, as it shifted medical knowledge from ancient theories to a more accurate and scientific understanding of human anatomy and physiology.

The other choices refer to important developments but do not pertain to Harvey's contributions. The invention of the microscope, for instance, is typically credited to scientists like Antonie van Leeuwenhoek, while the discovery of different types of blood cells came later with advancements in hematology. The stethoscope, another critical tool for doctors, was invented by René Laennec, not Harvey. Thus, Harvey's focus on blood circulation stands out as his vital achievement in the history of science.