The total solar eclipse on Aug. 11 will be visible in whole or in part to about 2 billion of the earth's residents. Medical experts are worried that millions might damage or destroy their vision by looking at the sun in the seconds before or after totality.

The nations that the arc of eclipse will pass over are arguing about what precautions people should take. In France, millions of pairs of cardboard-and-film sunglasses have been distributed. The British government, however, is warning people that glasses are inadequate unless the lens is Mylar and each pair is carefully guarded against scratching. Health officials in London are urging people to watch the eclipse on television -- a warning likely to be widely ignored in England's southwest corner, where the path of totality first passes over land.

Ophthalmological associations across Europe and Asia have been passing out postcards with a pinhole in the center, urging people to turn their backs to the sun and project the image of the eclipse onto white paper.

There are also fears that billions of farm animals, grazing at midday, will gaze curiously at the dark spot in the sky and will suffer for it when the sun emerges from the lunar shadow.