Don't hesitate. Cast it as far as you can.
From Fallen London Wiki
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From: Ring of Stone
The zee is black. The ring shivers in your hand.
Game Instructions: This will substantially reduce your Nightmares and increase your Dangerous quality.
Unlocked with 
1 x Ring of Stone
Success
The water takes it with a viscous gulp
Nothing happens. Have you just thrown an ancient artefact in the zee for no reason? Bubbles rise to the surface. Is that good?
That night you sleep better than you have in weeks, and wake confident. Probably the zee air.
Walking the Falling Cities is increasing… (+? CP, up to level 15)
You've lost 1 x Ring of Stone
Nightmares is dropping… (-7 CP)
Dangerous is increasing… (+5 CP, up to level 200 + 
Dangerous Gains)
