New Altitude Measurements for Aconcagua and the Ojos del Salado. In February, a team of Italian scientists from the University of Padua and Italian climbers, supported by the Argentine Institute of Glaciology and Nivology and Argentine climbers, made new measurements of the two highest peaks in the Americas, Aconcagua, which lies entirely in Argentina, and the Ojos del Salado, which is farther north on the Chilean-Argentine frontier. The project was under the direction of Francesco Santon. The surveyors employed GPS (Global Positioning System). This uses a constellation of earth-orbiting satellites and portable receivers. The receivers track and record the positions of many of the satellites simultaneously. In addition to a receiver being placed in an “unknown” location, such as a mountain summit, other receivers are placed at “known” positions, such as benchmarks. When all receivers are switched on, they record the positions of the overhead satellites, forming mathematical triangles. Using a form of triangulation, the position of the “unknown” receiver can be determined based on the “known” positions of the other receivers and the satellites. For the measurements of Aconcagua, the surveyors set up stations at Mendoza, Potre- rillos, Punta de Vacas, Cristo Redentor, Puente del Inca and Plaza de Mulas. For the Ojos del Salado, the stations were all in Argentina, at Cuesta de Reyes, Fiambalá, Cuesta de Loro Huasi, Chaschuli, Cazaderos Grandes, Aguas Calientes and Laguna Negro Pass. The height obtained for Aconcagua was 6962 meters (22,841 feet), which is 2.3 meters higher than the previous official altitude. They determined the altitude of the Ojos del Salado to be 6900 meters (22,628 feet), with a possible error of 5 meters. This is 15 meters higher than the previous official altitude of 6885 meters. It is not known by us if the respective governments have accepted the new altitudes as being official. As we go to press, Francesco Santon has been kind enough to inform us that he left Italy for the Andes on January 15, 1990 in order to refine the measurements of the Ojos del Salado.