Gamma rays and the origin of cosmic rays

A number of aspects of the relationship between gamma‐ray observations and the origin of cosmic rays are examined. The recent EGRET results of gamma rays from the Magellanic Clouds confirm our long held view that the bulk of the cosmic rays detected at the earth come from Galactic sources. The same conclusion comes from the inferred gradient of cosmic ray intensity in the Galaxy.A new analysis of long published gamma‐ray data from COS B at intermediate Galactic latitudes (‖b‖=11°→19°) leads us to believe that there are changes of both spectral shape and emissivity per struck nucleus with respect to longitude. The relevance of these results to the problem of cosmic ray origin and propagation, and to the calibration factor, X, which relates CO line intensity to column density of molecular hydrogen, is discussed.