On this day in music history: July 4, 1970 - “American Top 40” makes its debut broadcast on the ABC Radio Network. The show is hosted by radio personality Casey Kasem counting down the top 40 singles in the US as determined by Billboard Magazine. It is an instant success becoming one of the longest running radio shows in history and is still on the air today. Originally broadcast on only seven radio stations, by the 1980’s it will be carried on 520 stations in the US and heard in over 50 countries around the world. Kasem will host until 1988, then from 1998 to 2003.