Ferry's black body is an artificial black body designed by English physicist Horace Albert Ferry.

• A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.
• It neither reflects nor transmits any radiation and emits radiation based on its temperature, known as black-body radiation.

Ferry's black body is a closed cavity with a small hole. The inner walls are coated with a black material to absorb radiation. Radiation entering the hole undergoes multiple reflections and absorptions inside the cavity, ensuring nearly complete absorption. The small hole acts as an almost perfect black body, emitting radiation characteristic of its temperature.