The silver, being the anchor of every character's dream-ideal, now plays that role literally: Decoud clings to it as a physical relief from the unpredictable buffetings of the darkness. The terror of being "flung about" by the mysteries of the unknown makes one "instinctively" cling to any physical object, i.e., any dream-ideal, any society, at any price. Hirsch does exactly the same thing with the steamer's anchor below, with terrible consequences for him.