Centennial Exposition was the first ever international exposition held in Fairmount Park, US. Almost 10 million visitors attended the exhibition. The formal name of the exhibition was "International Exhibition of Arts, Manufactures and Products of the Soil and Mine".
In order to grab the attention of the scientific community and the general public to Bell’s innovations, he prepared a series of public demonstrations and lectures. His famous invention, the telephone got international attention as he demonstrated an early telephone prototype at the Centennial Exposition in Philadelphia in 1876. There were many influential visitors including Emperor Pedro II of Brazil in that exhibition.
Source: Wikipedia