Observations of the cosmic radiation arriving at the earth show that both the energy spectrum and total intensity of particles change with time. A brief survey is presented of the major changes in the flux of relativistic particles, with representative data from nucleonic detectors. The rigidity dependence and attenuation for the long-term change and transient variations are discussed. Some data for the sudden increases which represent solar injection are shown. The investigation of these intensity-time variations yields information about the electromagnetic state of the earth-sun region.