"Try as we may to make a silence, we cannot.
"For certain engineering purposes, it is desirable to have as silent a situation as possible. Such a room is called an anechoic chamber, its six walls made of special material, a room without echoes. I entered one at Harvard University several years ago and heard two sounds, one high and one low.
"When I described them to the engineer in charge, he informed me that the high one was my nervous system in operation, the low one my blood in circulation."
