ALL the recently discovered pulsating radio sources show apparently random amplitude variations on several time scales. The shortest is evident in the shape of individual pulse envelopes, and is almost certainly intrinsic to the source1. A second is an amplitude change from pulse to pulse; it is thought to be intrinsic also, although scintillations near the source may have some effect2. A third phenomenon is a much slower amplitude fluctuation with a time scale of about a minute at 100 MHz, and up to an hour at 400 MHz and higher. One explanation for this variation is scintillation, or refraction of the radiation by irregularities in the electron density in interstellar space3. In order to examine the spatial correlation of the latter two variations, simultaneous observations of the source CP 1919 were made on a common frequency at Stanford and Arecibo on April 22, 1968.