The strongest opponents of the upward tendency in pitch were singers, who complained that it was putting a strain on their voices. Largely due to their protests, the French government passed a law on February 16, 1859, which set the A above middle C at 435 Hz. This was the first attempt to standardize pitch on such a scale, and was known as the "diapason normal". It became quite a popular pitch standard outside France as well, and has also been known at various times as "French pitch", "continental pitch" or "international pitch" (the last of these not to be confused with the 1939 "international standard pitch" described below). An 1885 conference in Vienna established this value among Italy, Austria, Hungary, Russia, Prussia, Saxony, Sweden and Württemberg. This was then eventually included in the Treaty of Versailles in 1919. The "diapason normal" resulted in middle C being tuned at about .