 Hello, and welcome to our segment on elementary particles. An elementary particle is a particle that has no internal parts. In other words, it's a particle that has no other more elementary particles inside of it. We've seen two of those so far, the electron and the photon. In the last segment, scientists were reducing the 92 elements that made up all of matter down to three particles, the electron, the proton, and the neutron. In this segment, scientists went to the mountaintops and put bubble chambers up in balloons to find a vast array of new particles. We'll cover those particles in this segment. We'll also probe the proton, much like Rutherford was able to probe the atom. He found a nucleus inside. We're going to find some things inside the proton, but first let's take a look at the particles that were found from cosmic rays.