Einstein's theory of relativity, which he developed in the early 1900s, predicted changes in the passage of time for objects traveling at extremely high speeds. Very accurate clocks were put in airplanes and flown at extremely high speeds. When the planes landed, clocks in the planes were compared with ground clocks. The difference in the times on the clocks were just what was predicted by the theory. It inspires more confidence when two independent theories confirm one another.
Cosmic rays create new particles high in the upper atmosphere.
Observations showed that the particles did hit the earth. By using one of Einstein's equations in relativity theory it was shown that time slowed down for the particles traveling toward earth. The theory matched experimental results and both the theory of relativity and the theory of radioactive decay were supported. Anyone using proper procedures must be able to achieve the same results. A well respected scientist named Blondlot announced he had discovered a new ray, which he called an N-ray.