why are electromagnetic waves called perpetuating waves?
Since this is not my area of expertise, I searched Google under the key words "electromagnetic perpetuating waves" to get these possible sources:
http://www.everything2.com/index.pl?node=electromagnetic%20radiation
(Broken Link Removed)
http://howthingswork.virginia.edu/page1.php?QNum=540
http://cornellmath.wordpress.com/2007/08/08/why-stuff-is-hard/
http://www.rexresearch.com/hodorhys/emsigprp/emsigprp.htm
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search.
I hope this helps. Thanks for asking.