Everything is composed of "atoms", which are physically, but not geometrically, indivisible.
All matter was composed of atoms, indivisible and indestructible building blocks.
J. J. Thomson
I discovered the electron by experimenting with a Crookes, or cathode ray, tube.
The first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons.
Developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level.
Contributed to the wave theory of matter and to other fundamentals of quantum mechanics.