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Philip Glass composed this music for Sesame Street in 1979. It is not sampled from his other works. It has aired on Sesame Street as recently as 1994 and probably later. For the full details, see these articles on Muppet Wiki:
http://muppet.wikia.com/wiki/Geometry_of_Circles
http://muppet.wikia.com/wiki/Philip_Glass

Since this was uploaded, Sesame Workshop has uploaded one of the four cartoons to their official channel on YouTube. You can find it here:

http://www.youtube.com/watch?v=-9467zZV0Lc

Additionally, another short has been released on the vintage DVD collection Sesame Street: 40 Years of Sunny Days:

http://muppet.wikia.com/wiki/Sesame_Street:_40_Years_of_Sunny_Days