In two hours the muscles of the heart contract and relax, contract again and relax only eight thousand times. The earth travels less than an eighth of a million miles along its orbit. And the prickly pear has had time to invade only another hundred acres of Australian territory. Two hours are as nothing. The time to listen to the Ninth Symphony and a couple of the posthumous quartets, to fly from London to Paris, to transfer a luncheon from the stomach to the small intestine, to read _Macbeth_, to die of snake bite or earn one-and-eightpence as a charwoman.