Complex sentence: Bleriot was a spectator at Voisin's first trials of the floatplane glider he had built on 8 June 1905, and the success of these trials prompted him to commission a similar machine from Voisin, the Blériot II glider.
Split into simpler sentences: Bleriot was a spectator at Voisin's first trials of the floatplane glider he had built on 8 June 1905. The success of these trials prompted him to commission a similar machine from Voisin, the Blériot II glider.