If our eyes only saw frames (IE: 30 images a second), like a single lens reflex camera, we'd see images pop in and out of existance and that would really be annoying and not as advantagous to us in our three dimensional space and bodies.
In the Vienna of the second half of the 18th century, in addition to Haydn and Mozart, three symphonic composers, namely Leopold Hoffmann, Carl Ditters von Dittersdorf and J.B. Vanhal helped further the development of the symphony.
A symphony is a large, multi-movement work for orchestra. It calls for instruments from all four sections (winds, strings, percussion, and brass) and explores a complete range of melody, harmony, rhythm, dynamics, and timbre. That seems like a basic definition, but even that already has a number of exceptions. The symphony really came into existence with the Classical period and Haydn.