Just as Rossi left Eritrea, he received news of two observations of a similar east–west effect. These were published in the Physical Review. One was by Thomas H. Johnson, and the other was by Compton and his student, Luis Alvarez, who reported observations at Mexico City, where the latitude is 19° N. Because others had carried out the first experimental exploitation of his important idea of 1930, Rossi was disappointed, but published his results immediately after returning to Padua. Later, with Frederick C. Chromey, Alvarez and Rossi patented a "Vertical Determination Device", which made use of cosmic ray telescopes.