The bell is sounding in a glass enclosure, and gradually to the glass in the pump pumping air, we heard more and more _, finally almost _, reasoning: when vacuum hood (without air), we will _.
Is the bell sound, bell vibration. Air and glass is less, the bell sound more and more small, the air is completely out, when a vacuum is drawn, the sound will disappear; the ACD does not meet the B. problem;
Small; unable to hear sounds
