Seven of the sculptures in this series were marble, while the remaining nine were bronze casts. When some of the bronzes in this sculpture group were imported to the US, they became the subject of a legal case because non-representational art was not considered art, triggering an attempt to place a tariff on the sculptures. Identify this series of sculptures created in the 1920s and 1930s by Romanian-born French sculptor Constantin Brâncuși.
Bird in Space