Compass reversal

Compass reversal is the late-discovered change in the expedition’s compass polarity that explains its apparent failure as a guide. The needle had pointed north even as the travelers emerged from the underground world at Stromboli, and neither Henry nor Professor Hardwigg could make the instrument’s indication agree with their presumed route. Only after six months, when Henry examined the compass again, did they recognize that its needle actually pointed south. They traced the reversal to the ball of fire in the Central Sea storm, which had magnetized the iron in the raft. The solution corrects their reading of the journey and ends Professor Hardwigg’s lingering intellectual distress.

The compass as a problem of orientation

During the final ascent from the volcano, Henry and Professor Hardwigg confront a geographical contradiction. Henry imagines that they have crossed half the globe and reached the antipodes of Europe, but his uncle insists that the compass had always indicated north. Henry cannot reconcile that reading with the route he thinks they have taken; he admits there is no possible explanation. The compass, an instrument expected to make direction measurable, instead makes their location less intelligible.

The contradiction persists after the travelers reach the surface. As they continue toward the port of Stromboli, Professor Hardwigg mutters that the compass certainly marked north, a fact he cannot explain. The question does not end with their escape from the earth’s interior: it follows them into the account of their return and stands apart from the other consequences of the expedition. The instrument has served as a practical guide, but its apparently stable indication now threatens the geographical interpretation of the whole voyage.

The delayed discovery

The explanation comes not during the return journey but after it. Six months pass with the famous compass lying unnoticed and untouched. When Henry happens upon it while Professor Hardwigg is arranging minerals from his collection, he examines the instrument closely and sees that its needle points south rather than north. The decisive evidence is physical and immediate: the compass is not merely giving an inconvenient reading; its poles have changed.

Professor Hardwigg initially doubts Henry’s observation, then puts on his spectacles and examines the instrument himself. Recognition turns bewilderment into joy. He reconstructs the turning point as the expedition’s passage beyond Cape Saknussemm: after that point, he says, the needle pointed south instead of north. This retrospective reading makes the final geographical confusion legible. Their earlier assumption that the needle retained its ordinary orientation was wrong, so its indication could not be used as they had used it to judge their direction.

The cause and its consequences

Henry attributes the change to the storm on the Central Sea. During that storm, a ball of fire struck or affected the raft’s iron, magnetizing it and turning the compass topsy-turvy. Professor Hardwigg accepts the explanation as a trick of inexplicable electricity. The episode links a dramatic natural event to the humble instrument that had seemed to record the travelers’ course: the storm did not simply disrupt the voyage, but altered the means by which they understood where they were going.

The reversal resolves a specific puzzle rather than accounting for every feature of the underground world. It explains why the compass’s northward indication could coexist with the expedition’s eventual emergence on Stromboli, and why Professor Hardwigg’s confidence in the instrument had led to an apparent impossibility. The explanation also depends on delayed inspection. The compass remains available throughout the aftermath, but its changed polarity goes unnoticed until Henry looks at it again; the answer is present in the object before the travelers can read it.

Resolution and narrative significance

The compass reversal gives the expedition a final act of interpretation after its physical return. The explorers have escaped, the journey has become an international sensation, and Professor Hardwigg has received public recognition, yet the compass remains an unresolved wound in his scientific self-understanding. Its altered needle has made the return seem inexplicable precisely because the instrument had appeared to offer reliable evidence. Henry’s discovery turns that contradiction into a solvable material cause, and Professor Hardwigg’s ensuing delight closes the question that had preyed on him.

The reveal also preserves a productive distinction between observation and explanation. The needle’s southward direction is directly visible; its alteration is confirmed when Professor Hardwigg inspects the compass. The account of how the Central Sea storm magnetized the raft’s iron is Henry’s causal interpretation, which Professor Hardwigg embraces. Thus the ending does not erase the earlier confusion: it shows how a changed object, left unexamined, can make trustworthy observations support a false account of direction. The compass’s failure is not that it points nowhere, but that its altered polarity is mistaken for its former one.