This booklet is the fourth in a series of nine that describe the Apollo-Soyuz mission and experiments. This set is designed as a curriculum supplement for teachers, supervisors, curriculum specialists, textbook writers, and the general public. These booklets provide sources of ideas, examples of the scientific method, references to standard textbooks, and descriptions of space experiments. There are numerous diagrams, as well as questions for discussion (with answers) and a glossary of terms. The series has been reviewed by selected high school and college teachers nationwide. This booklet discusses the Doppler Effect, the earth's gravity anomalies, the "low-low" satellite technique, and the "high-low" satellite technique. (MA)