This was a different passage of the Inner Vortex ascending as compared with the same 28 days before. At that date (June 22) it did great damage in the central parts of Illinois. Still this last passage was very palpable—the clouds were very irregularly assorted—plates of cirrus above and beneath cumulus—various kinds of cirrus clouds, and that peculiar prismatic haze which is a common sign of the passage of a vortex. The appearance depicted above is a very common, although a very evanescent appearance. When the sky appears of a clear blue through the cirri, there will be generally fresh gales without any great electrical derangement; but if the clear spaces are hazy, gradually thickening towards the nucleus, a storm may be expected. Any one who wishes to understand the indications of the clouds, must watch them closely for many years, before he can place much reliance upon them. But we shall again advert to this point.
We have now passed through one sidereal period of the moon. We might continue the record, but it would be tedious. The passages of these vortices vary in violence at different times, as we might expect; but they never cease to circulate, and never will as long as the moon remains a satellite to the earth; and if we take the passage of any of these vortices, and add thereto the time of one sidereal period of the moon, we get approximately the time of the next passage. When the elements of the lunar orbit tend to accelerate the passages, they may come in 26 days; and when to retard, in 28 days; and these are about the limits of the theory.
Having begun and ended this record of the weather with the passage of the Inner vortex ascending, it may not be amiss to notice one more, (the August passage,) as it offers a peculiarity not often so distinctly marked. We have alluded to the greater force of the storms when the passage of the vortex corresponds to the passage of the line of low barometer or the depression point of a great atmospheric wave, which is also due to the action of the ether. In consequence of these waves passing from west to east, the storm will only be violent when formed a little to the westward. If the storm forms to the eastward, we neither see it nor feel it, as it requires time to develop its strength, and always in this latitude travels eastward; so that storms may generally be said to come from the west, although the exciting cause travels from east to west. In the case now alluded to, the weather indicated a high barometer, and the storm formed immediately to the eastward, even showing a distinct circular outline. We subjoin a description.
August 15th. Clear morning (N.-E.), a bank of cumuli in south: noon quite cloudy in S. and clear in north. (N.-E.)
16th. Clear morning (N.-E.); 3 P. M., getting very black in E. and S.-E., very clear to the westward; 4 P. M., much thunder and lightning in east, and evidently raining hard; 5 P. M., a violent squall from east for 10 minutes; tore up several trees; 6 P. M., the storm passing eastward, clear in west all this time; 6.30 P. M., the storm forming a regular arch, the vertex being in S.-E.; the arch of hazy cirrus and heavy cumulus much lower in S.-E., wind still moderate from east; 10 P. M., clear all around, but lightning in S.-E. and E.
17th. Fine clear morning (W.); noon, scattered cumuli in north; 6 P. M., a beautifully regular arch of dense cumuli and cirrus margin in N.-E., with a constant glimmer of lightning; 7 P. M., very clear to the west, and north-west, and south; along the northern horizon a line of high peaked cumuli terminating in N.-N.-W.; a continued roll of distant thunder in the circular bank in N.-E., and not a moment’s cessation to the lightning; the electric excitement advancing westward along the lines of cumuli; the cirrus haze also rising and passing towards S.-W.; 8 P. M., the sky alive with lightning, the cirrus now reaches the zenith; no streaks of lightning coming to the earth; they seem to radiate from the heaviest mass of cumuli, and spread slowly (sufficiently so to follow them) in innumerable fibres over the cloudy cirrus portion of the sky; every flash seems to originate in the same cloud; 8.30 P. M., one branching flash covered the whole north-eastern half of the sky, no leafless tree of the forest could show so many branches; 9.30 P. M., all passed to S.-W. without rain, leaving behind a large cumulus, as if it lagged behind. From this cumulus a straight line of lightning shot up 10° above the cloud into a perfectly clear sky, and terminated abruptly without branching.
We have been thus particular in giving these details, as this was a clear case confirming the principles advanced, that the vortices do not form a continuous line of disturbance, in their daily passage around the earth. It shows also that the barometer, in connection with these principles, will be a far more useful instrument than it has yet proved itself, for practical service as an indicator of the weather.
FOOTNOTES:
[10]For convenience to those wishing to verify the calculation of these triangles, we have put down each side and angle as found. Also, as an aid to the navigator.
[11]Daily Wisconsin, July 7.