Despite the several experimental and theoretical studies that have been devoted to the investigation of the Fermi surface of beryllium, certain problems remain elusive in connection with the behavior of the electrons in beryllium single crystals. Only recently, for example, has magnetic breakdown in beryllium been investigated in detail, although its onset in fields of 50 kOe was discovered as far back as 1963.1'2 Beryllium is well known as one of the lightest of the elements; it has a low atomic number, and its atoms have only four electrons. Elements of this nature exhibit good agreement between the theoretical calculations of the Fermi surface and the experimental data. Metallic beryllium has relatively few carriers in the conduction band and, accordingly, a low density of carrier states at the Fermi level. Beryllium also has a small electron heat capacity; the coefficient associated with the linear term of its heat capacity has a value ~ = 0.4 x 10 -4 cal/mole • deg2. 3 Beryllium is a metal characterized by a high Debye temperature, which, according to Ref. 3, is equal to (1480 _+ 16)°C. The end result of the low density of states of the electrons and high Debye temperature is that a number of quantum effects are far more pronounced in beryllium than in most other metals. This feature renders beryllium a useful and fascinating medium for the investigation of such effects as magnetic breakdown. It has proven feasible in beryllium, for example, to study magnetic breakdown over a wide range of temperatures and to observe the socalled "thermal" breakdown effect) '4 A fair number of papers have been written to date on the subject of magnetic breakdown (see, e.g., the survey in Ref. 5), but a great many striking characteristics of this intriguing effect have not been unequivocally explained and are in need of further study. As the magnetic fields in which measurements are possible are increased, new possibilities are opened up for the investigation of magnetic breakdown, which is rapidly becoming one of the most interesting problems of the modern physics of l~etals. Another absorbing facet of magnetic breakdown is that it is one of many phenomena in which coherent quantum effects are strongly manifested. The study of various relevant factors and how they influence magnetic breakdown is there-