Part 16

9 59 30 Arcturus in the middle of the band; very bright and regular in outline, and widest at the zenith.

10 0 30 Arcturus on northern edge; north side better defined than the southern.

10 2 0 Arcturus 1d north; very bright.

10 2 30 Gamma and Delta Leonis, northern edge.

10 3 Regulus on southern age; getting faint.

10 5 Fast fading away.

10 5 30 Scarcely visible; bank in north faint.

This aurora was due to the inner vortex ascending, whose period was at this time 28 days.

There are several circumstances to be observed in this case. The bow brightened and faded simultaneously with the aurora, and respected the vertex of the auroral bank, being apparently concentric with it. The bow, therefore, depends on the same cause, but differs from the aurora in being limited to the surface of the atmosphere in which the vortex has produced a wave to the southward of its central path, as may be understood by inspecting Fig. 2, Sec. 1,--the figure representing the polar current of the central vortex. On the 29th of May, 1840, the author saw a similar phenomenon, at the same time of night, and passing over the same stars southward until it reached within 5d of Jupiter and Saturn, to which it was parallel. This atmospheric wave offers a greater resistance to the passage of the ether: hence the light. On this account it is, also, that when the passage of a vortex is attended by an auroral display there will be no thunder-storm. There may be an increase of wind; but the atmosphere at such times is too dry to make a violent storm, and there is a silent restoration of the equilibrium, by the ether passing through the dry atmosphere, without meeting any condensable vapor, and becoming luminous on account of the greater resistance of the air when unmixed with vapor. We thus see also the connection between the aurora and the linear cirri, and we have a triumphant explanation of the fact, that when the observer is north of the northern limit of the vortices, he sees the aurora to the south and not to the north; for, to see it to the northward, he would have to see it in the same latitude as it appears in the south, and, consequently, have to see across twice the complement of the latitude. We thus see, also, why the temperature falls after an aurora; for, the passage of electricity in any shape, must have this effect on account of the great specific caloric of this fluid. We see, also, why the aurora should be more frequent where the magnetic intensity is greatest and be consequently invisible at the equator, and why the magnetic needle is so sensibly affected at the time of its occurrence. We may, perhaps, here be allowed to allude to another phenomenon connected with terrestrial magnetism and electricity.

EARTHQUAKES.

The awful and destructive concussions which sometimes are produced at great depths beneath the surface of the soil, would seem to indicate that no force but that of electricity is adequate to account for the almost instantaneous desolation of wide tracts of the earth's surface. But we do not mean to say that the action of the terral vortices, combined with the internal conditions of our planet, is the only cause; although it is far from improbable that the same activity of the ether, which generates through these vortices, the full fury of the hurricane in the tropics, may be simultaneously accompanied by a subterranean storm. And physicists are too rash to reject the evidence on which the connection of the phenomena rests.

In the extract given by Colonel Reid, in his "Law of Storms," from Sir George Rodney's official report of the great hurricane of 1780, it is stated, that, "Nothing but an earthquake could have occasioned the foundations of the strongest buildings to be rent; and I am convinced that the violence of the wind must have prevented the inhabitants from feeling the earthquake which certainly attended the storm." Again, in the Savannah-la-Mar hurricane, which occurred the same year and month, the Annual Register, published at Jamaica, states, that at the same time, "a smart shock of an earthquake was felt." The general serenity of equatorial regions is due to the fact that they are beyond the limit of the vortices, as in Peru, where neither rain nor lightning nor storm is ever seen. Thunder and rain, without storms, however, are common in other tropical countries, also out of the reach of the vortices. But even in those parts, (as the Antilles,) lying in the track of these vortices, the weather is not as frequently disturbed as in higher latitudes. The storms of the Antilles, when they do occur, however, are fearful beyond any conception, showing the presence of some cause, auxiliary to the ordinary disturbing action of the vortices, which, when simultaneously occurring, adds tremendously to their force.

That earthquakes are preceded sometimes by a peculiar haziness and oppressiveness, similar to that which sometimes precedes a storm, is a current opinion in volcanic countries. And Humboldt, who doubts the connection, has to confess that sudden changes of weather have succeeded violent earthquakes, and that "during the great earthquake of Cumana, he found the inclination of the needle was diminished 48'." He also mentions the simultaneous occurrence of shocks, from earthquakes, and a clap of thunder, and the agitation of the electrometer during the earthquake, which lasted from the 2d of April to the 17th of May, 1808; but concluding that "these indications presented by clouds, by modifications of atmospheric electricity, or by calms, cannot be regarded as generally or necessarily connected with earthquakes, since in Peru, Canada, and Italy, earthquakes are observed, along with the purest and clearest skies, and with the freshest land and sea breezes. But if no meteorological phenomena indicates the coming earthquake, either on the morning of the shock or a few days previously, the influence of certain periods of the year, (the vernal and autumnal equinoxes,) the commencement of the rainy season in the tropics, after long drought, cannot be overlooked, even though the genetic connection of meteorological processes, with those going on in the interior of our globe, is still enveloped in obscurity."

It is at the equinoxes that the earth changes her distances from the sun most rapidly, and whether she is passing from her perihelion or from her aphelion, the density of the ether externally is changing in the subduplicate ratio of these distances and consequently at these times there will be the greatest disturbance of the electric equilibrium. How far our views of the internal structure of our globe, (considered along a diameter as a solid crust, then a fused mass separated from the lower ocean by another solid crust, and separated from a similar arrangement on the opposite side by an interposed mass of water, perhaps also possessing a solid nucleus,) may affect this question, is difficult to say; but that the agent is electric, appears highly probable; and very recently it has been discovered, by M. Ratio Menton, that a piece of iron, suspended by attraction to a magnet, will fall on the approach of an earthquake; thus indicating that the power of the magnet is temporarily weakened by the action of some disturbing force.

FOOTNOTES:

Hum. Cosmos, art Aerolites.

We shall in all cases use this abbreviation for the extremely awkward word zodiacal.

It is here assumed, that all the vortices are at their apogee at the same time, and, consequently, they lie in different longitudes, but the central being between, its position is taken for the average position of the three.

It is far from improbable that the effect produced in one zone of climate, may be reversed in another, from the nature of the cause.

That the 11th, 12th, and 13th of May should recede 2d in temperature as determined by Maedler from observations of 86 years, at a time when the power of the sun so rapidly augments, is strongly confirmatory of the theory. See Cosmos, p. 121.

Plucker first discovered that a plate of tourmaline suspended with its axis vertical, set axial.

Silliman's Journal for March and April, 1853.

Humboldt, Cosmos p. 193, London ed.

See Silliman's Journal for September, 1853.

See Silliman's Journal for September, 1853.

This was the central vortex ascending.

Reid's Law of Storms, p. 350.

Humboldt, Cosmos, p. 203.