One of the central dogmas of modern science is that the world around us can be understood in terms of microscopic chemical entities known as atoms. It may come as a surprise that this notion has only been widely acknowledged since the 1910s. The French physicist Jean Perrin had a hand in many of the key developments that led to the emergence of the atomic doctrine. His life story relates how new technologies were used to 'see' these invisible particles of philosophy and how scientists were able to determine their size and composition. The indivisible atoms of the ancients were replaced by the highly structured elements of chemistry.