A combination of sensitive and insensitive photographic emulsions is used to improve the accuracy of measurement of the specific energy loss of relativistic nuclei. In recent years, various new theories of the origin of cosmic rays have been proposed. These proposed theories are classified according to the proposed mechanism for acceleration of the nuclei of the primary cosmic radiation or according to the assumptions made concerning the source region. The most abundant elements in the known universe are hydrogen, helium, carbon, oxygen, nitrogen, magnesium, and silicon. This chapter focuses on the production of lithium, beryllium, and boron fragments in energetic collisions between nuclei. The nuclear fragments of an average star produced by a singly charged particle in the light nuclei of the emulsion must carry 7.95 units of charge, assuming a contribution from carbon, nitrogen, and oxygen nuclei proportional to their geometric cross-sections. The absence or scarcity of lithium, beryllium, and boron nuclei in the primary radiation indicates that as far as the distribution between light and heavy elements is concerned, the chemical composition at the source is similar to the average chemical composition of the universe.