Atoms are considered invisible, yet their structure is understood through historical experiments, notably the Rutherford and Bohr models, which laid the groundwork for modern quantum mechanics. The Rutherford model introduced the concept of a nucleus surrounded by electrons, while the Bohr model explained electron orbits without energy loss. Additionally, Einstein's explanation of Brownian motion illustrates how invisible atoms interact with visible particles, providing evidence of their existence. The discussion emphasizes the importance of foundational knowledge in physics and encourages further inquiry into the subject. Understanding these concepts is essential for grasping the nature of matter.