Thomas Edison didn't formally study in a specific area of science in the traditional sense. He was largely self-taught and his interests spanned a wide range of fields.

However, his most notable work was in the realm of electrical engineering, particularly applied electricity and electrical lighting.

He also made significant contributions to:

* Telegraphy: He started his career as a telegraph operator and later developed improved telegraph systems.

* Sound recording: He invented the phonograph.

* Motion pictures: He was a pioneer in the development of motion pictures.

* Chemistry: He experimented with various chemicals, including those involved in the creation of batteries and lightbulbs.

While Edison wasn't a formal scientist in the academic sense, his prolific inventions and contributions to various fields solidified his place as a crucial figure in the history of science and technology.