Most sources of inllumination generate light over an appreciable period, and indeed if and object is lit for a very brief time(less that 1/25 second), the human eye will not react in time to see the object. A photographic emulsion---that is, a light-sensitive coating on photographic film, paper, or glass---will, however, record much shorter bursts of light . A photographic flash can therefore be used in 1864, was a paper bag containing magnesium wire and some oxygen-rich substance, such as potassium chlorate. When the bag was ignited, the metal burned with an intense flash. A worse that engulf the room in dense smoke and lead to pictures of dubious quality and odd poses