1956 "Second Impression"; The John Day Company publishers; hardbound; very good condition of book; original owners name inside front (pic); very good condition of dust jacket with very minor edge wear.
 
description -
The boys go exploring in the Pacific, this time studying volcanoes as the companions of a young scientist. With him they share some astonishing [feats]: they are let down into a boiling crater in a steel and glass ball; they investigate an active crater on the bed of the sea; they help to recue the people of doomed 'Tin Can Island'. But the scientist's strange behaviour increases the dangers of their already hazardous project...