GROUND-BASED GAMMA-RAY ASTRONOMY

Ground-based gamma-ray astronomy has slowly developed over the past qu arter of a century to a position now where a number of sources are kno wn to produce gamma-rays in the energy range 10(11)eV to 10(18)eV. The observations are difficult, with exceptional signal to noise problems , but improved techniques are now allowing observers to proceed with c onfidence. In this paper the physical bases of the observations are em phasised to show the important issues in the field and the present sta te of the observations is indicated.