When practical people asked George Mallory why he wanted to climb Mt. Everest, the Englishman answered; "Because it is there." French Naval Captain Jacques Y. Cousteau is a man similarly obsessed; his obsession, however, is with the depths of the sea.

Cousteau and his companions are the forerunners of a new era of undersea exploration. Using the remarkable aqualung, a light apparatus which supplies the diver with compressed air, they were able to plunge to depths of over three hundred feet, where the pressure is capable of crushing a submarine. Through Costeau's engrossing account and his starting photos, the reader can share in some measure the fascination of the curious realm of silence--a world of unknown colors, of sunken ships and playful octopi.

In the teeming life of the deep sea, the divers found far fewer terrors than the reader might expect. Cousteau takes pleasure in debunking the usual tales of sea monsters, having found the octopus an agreeable playmate and giant rays, moray eels, and even "killer" sharks most uninterested in the human invaders.

From one danger, however, even the aqualung could not secure the divers--the drunken elation induced by nitrogen gas under the tremendous pressures of the depths. In the intoxication of the "zone of rapture", the diver may lose control, as one of the group did, and tear the aqualung from his back as an impulsive gift to a passing fish.

The aqualung, of which Cousteau was co-inventor, has opened to the "men fish" depths which only the imagination of Jules Verne has explored before. "The Silent World" opens them to the reader as well