More than once the accuracy of the enemy's fire drove the little party to shelter. Though the diver was shielded by the impenetrable fickle element that gave Achilles invulnerability, the air-pump above was exposed, and thus the diver might be slain by indirection. There lay Achilles' heel, the exposed vulnerable part that Mother Thetis's baptism neglected. The work below was arduous: the hulk crowded with the entangling machinery of sixteen engines, cuddies, ports, spars, levers, hatches, stancheons, floating trunks, bibulous boxes heavy with drink, and the awful, mysterious gloom of the water, which is not night or darkness, but the absence of any ray to touch the sensitive optic nerve. The sense of touch the only reliance, and the life-line his guide. But the peril incurred can be better understood through an illustrative example of a perilous adventure and a poor return. Officers and men of the unfortunate monitor asked for the rescue of their property, allowing a stipulated sum in lieu of salvage. Among these was a petty officer, anxious for the recovery of his chest. It involved peculiar hazards, since it carried the diver below the familiar turret-chamber, through the _inextricabilis error_ of entangling machinery in the engine-room, groping among floating and sunken objects, into a remote state-room, the Acheron of the cavernous hold. He was to find by touch a seaman's chest; handle it in that thickening gloom; carry it, push it, move it through that labyrinthine obscurity to a point from which it could be raised. To add immeasurably to the intricacy of this undertaking, there was the need of carrying his life-line and air-hose through all that entanglement and obscurity. Three times in that horror of thick darkness like wool the line tangled in the web of machinery, and three times he had, by tedious endeavor, to follow it up, find the knot and release it. Then the door of the little state-room, the throat of exit, was shut to, and around and around the dense chamber he groped as if in a dream, and could find no vent. All was alike--a smooth, slimy wall, glutinous with that gelatinous liquid, the sea-water. The tangled line became a blind guide and fruitful source of error; the hours were ebbing away, drowning life and vital air in that horrible watery pit; Aut hoc inclusi ligno occultantur Achivi,