Greetings,
Still powerful and inspiring :
http://www.zakros.com/mica/soundart/s04/varese_text.html
Or as a PDF if you prefer:
http://music.arts.uci.edu/dobrian/CMC2009/Liberation.pdf
Much has been written of Varese's prescience regarding music and
machines. I've read The Liberation Of Sound many times through the
years, and it still amazes me, as does his wonderful music.
Highly recommended reading.
Best,
dp