In music notation what specifies the number of beats in a bar

Theres a certain thing on the music called a time signature . this specifies the certain beats per measure 

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You do not see contemporary artist using chiaroscuro as much anymore, because it was used at a time when there were only candles and firelight for nighttime illumination. many of the paintings that used chiaroscuro did so to depict people who were around candlelight. this to illuminate their forms and create a dramatic effect. because we have modern electricity and light, the technique isn't seen as frequently in present day art.