44
THE
ERUPTION
OF
PELÉE
the earth, which in t u r n gave rise to the magnetic disturbance observed on the earth's surface. We have had, namely, repeated instances in which seismic disturbances, known to have occurred, were recorded not on seismographs, b u t on magnetographs. This might occur if, for example, the mechanical displace ment of masses below the surface resulted in either the formation, destruction, or redistribution of the electric currents, which in t u r n produced the magnetic effect. This magnetic effect would then propagate itself more rapidly to the surface of the earth t h a n the mechanical vibration, and hence might be recorded first or even give a record when the mechanical vibrations b y the time they reached the earth's surface would be too feeble to leave their trace on seismo graphs. " However, in the case of the magnetic disturbance before us no such simple explanation is possible. While the mathematical analysis has not yet been com pleted, it has progressed sufficiently far to show t h a t the cause of the magnetic disturbance cannot be referred to any distribution of electric currents below the earth's surface, b u t that, on the other hand, the observed phenomena are better satisfied b y assuming a distribution of electric currents in the regions above us. As is known, it is with the aid of the changes in the vertical component of the earth's magnetism t h a t we can decide whether the forces producing the observed disturbance have their seat in the earth's interior or in the regions outside. The question now is, was the coincidence between the magnetic disturbance and the Mt. Pelée eruption a mere chance connection? If not, then the further analysis of the magnetic disturbance is going to be of the greatest interest. " T h e production of static electric charges b y the rapid ejection of parti cles of steam or vapor is well known. I t m a y thus be possible t h a t the violent and tremendous ejection of vaporous particles from within the volcanic cone produced such a high electrification of the regions above the volcano as to have sufficiently altered the potential of the semi-permanent electrification of the upper regions to have immediately produced an inflow or outflow from out side space of electric charges so as to make the resultant effect comparable to t h a t associated with a magnetic storm coming from without. I t will be recalled t h a t the products ejected b y the eruption were described to be principally of a vaporous or gaseous character and finely powdered ash. All reports dwell espe cially upon the electric flashes over the mountain during the eruptions. " I f it is possible, therefore, to disturb the entire earth's magnetism b y an explosion on the earth, our conceptions as to the manner of the connection of magnetic disturbances and solar eruptions have had some light shed upon t h e m . " The suggestion of Bauer, based upon the preponderating change in the hori zontal component of the earth's magnetism, t h a t the seat of the magnetic dis turbance was more likely to have been exterior to the earth t h a n interior, is interesting, and leads to the inquiry as to what possible condition could have been so abruptly imposed upon the outer shell of our planet as to permit of a universal magnetic disturbance being brought about in an almost identical instant of time. Dr. Bauer, as the quotation from his writings shows, sees the