This is a study of ontology.
Ontology is a general study of substance.
Albert Einstein considered himself to be an ontologist. In general though, scientists who study chemistry and elementary physics do not consider themselves ontologists, because they have limited their studies to phenomenal substance manifesting as matter. Atomism is still vigorously pursued today by modern high-energy physicists. Thales was known as one of the Seven Sages of Greece. He was also renowned as a mathematician, statesman and astronomer.