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The following table shows the mean two hourly tensions for three years, at Kew, viz.:
From this it will be seen that the tension of electricity is at a minimum at 4A.M., also, that it rises till 10, falls till 4P.M., but not as rapidly, rises till 10, falls again till 4A.M., or the close of the meteorological day—having two maxima and minima, as have most of the phenomena thus far considered.
In order to see what the connections between these ever-present, daily phenomena are, and their connection with other phenomena, and that we may understand their normal conditions, I will trace them approximately in a diagram (figure17.)
The foregoing diagram of the daily phenomena of a summer’s day, when no disturbing causes are in operation, no storm existing within influential distance, and no unusual intensity or irregular action ofany of the forces present, affords a basis for considering the various phenomena of the weather in all its changes and conditions.
It is obvious that the other phenomena do not all depend upon temperature merely, if indeed any of them do.
Temperature has but one maximum and minimum, and that is exceedingly regular, and does not correspond with any other.
The barometer has two; electric tension, two; magnetic activity, two; condensation, two—one the formation of cloud, and the other the formation of fog and dew; wind, one—resembling temperature in that respect, but embracing a much less period.
Fog forms at one barometric minimum, and cloud at another.
Fog forms at one period of the magnetic variation, cloud at another.
The formation of cloud corresponds with the greatest intensity of magnetic action, and its associate electricities. But the oscillations of the barometer do not correspond with either. And thus, then, we connect them:
This connection is equally obvious if the order is reversed—thus;
If we examine still more particularly the different phenomena, we shall find the same relative action of the forces carried into all the atmospheric conditions, however violent.
1. The barometer falls when horizontal magnetic force, and a tendency to cloud and wind, increase; and rises when they decrease. This corresponds with the character of the irregular barometric oscillation. Barometric depressions accompany clouds and winds, and are in proportion to them, and are all greatest where magnetic force is greatest. The barometer also rises as the magnetic energy decreases. Do the magnetic currents, passing upward with increased force, lift, elevate the atmosphere? How, then, are we to explain the increased range of the oscillations, as the center of atmospheric machinery is reached, where magnetism has least intensity, and the perpendicular currents are less, and attraction is less? Attraction is greatest where intensity is greatest, and there the barometer stands highest, and the diurnal range is least. Is it then the attraction of magnetism which produces the barometric oscillations? If so, how then can we explain the diurnal fall while magnetism is most active?
Perhaps we have not yet arrived at such a knowledgeof the nature of magnetism as is necessary to a correct answer of those questions. Faraday has taught us that the lines of magnetic force are close curves, passing into the atmosphere, and over to the opposite hemisphere, and returning through the earth, out on the opposite side in like manner, and back again, passing twice through the earth and twice through the atmosphere. All we know of this is what the iron filings indicate, and we do not know how much reliance to place upon the indications they give. But if Faraday is right, the sun will, twice each day, intersect and stimulate into increased activity the same closed magnetic curve—once when it is coming out of the earth, during our day, when its influence will be the most active, and once when it is returning on the opposite side of the earth; and a second, but feebler magnetic and electric maximum, may be occasioned by its action on the opposite and returning closed curve of the same current. However this may be, it is exceedingly difficult to conceive, of any adequate influence exerted by the tension of vapor.
So the mid-day barometric minimum may be caused by the attraction of the earth, in a state of increased magnetic activity and intensity, upon the counter-trade, and its consequent approach or settling toward the earth. Observation, as I have already said, pointedly indicates such a state of things. So the increased magnetic activity, with or by its associate electricity, acts upon the electricity of the counter-trade, condensation takes place, the electricity is disturbed in the surface-atmosphere, by induction, andits tension is changed. Opposite electrical conditions are induced in the surface strata, and attraction takes place. The air moves easily, and thus the attractions originate the winds. Secondary currents are induced, as in all other cases of electric activity, and winds, indifferent strataand directions, occur, with or without cumulus, or scud condensation, according to their activity, and the proportion of moisture of evaporation they may contain.
I am well aware that the various received theories of meteorology attribute condensation to the action of cold, mingling of colder strata, etc. But I think that view will have to be abandoned.
It assumes that moisture is evaporated and held in the atmosphere by latent heat, which is given out during condensation, and actually warms the surrounding atmosphere. Thus, the Kew Committee undertook to explain the development of greater heat, at the elevation where they, in fact, found the counter-trade. But how unphilosophical to suppose a portion of the air or vapor contained in it, can give out to another adjoining portionmore heat than is necessary to produce an equilibrium. This can, indeed, be done by experiment—but the experiment is made with currents of electricity. How unphilosophical, too, to talk of latent heat in connection with evaporation,at the lowest temperature known. Meteorologists must revise their opinions on the subject of condensation. This latent heat has never been actually met with; on the contrary, the most sudden and complete condensations of the vapor of the atmosphere are attended by as sudden and extraordinary productionsof cold, and consequent hail, and the connection between condensation and electricity is shown by too many facts to permit the old theory to stand.
Fog never forms with the thermometer below 32°.It is mainly asummer condensation, especially high fog. It has been attributed to the cooling effect of an atmosphere colder than the earth, but it often occurs when the earth is the coldest, and when the vapor, as it rises, is colder than the air, and could not give out heat to a warmer medium. (See American Journal of Science, vol. xliv. p. 40.) Again, it is not mere condensation, but a formation of globules or vesicles, hollow, and the air expanded in them, by means of which they float like a soap bubble which contains the warm air of the breath. Is not every vesicle a model shower, positively electrified on the outside, negatively in the center, or the reverse, according to the strata, with the air expanded in the middle by the excess of heat which negative electricity detains? Look at them, as they attach themselves to the slender nap of the cloth you wear, when passing through them, and see how many of them it would require to form a large drop of rain. The clouds are of a similar vesicular character, and rain does not fall till the vesicles unite to form drops. Sudden and extreme cold is indeed produced in the hail-storm, when, above, below, and around it, the temperature is unaffected. Testu, Wise, and other aeronauts, have so found it, and the hail tells us it is so. But it is idle to say it results from radiation. All the phenomena of the sudden, violent hail-storms are electric in an extraordinary degree.The electricity is disturbed and separated—the associated heat continues with the negative, and leaves the positive portion of the cloud, and a corresponding reduction of temperature results. So Masson found in his eudiometrical analytical experiments thenegativewire would heat to fusion, while the positive was cold. (See London, Edinburgh, and Dublin Journal of Science for December, 1853.) This disturbed electricity is diffused over the vesicles. Listen to the thousandcracklingsounds which initiate the clap of thunder, and may be heard when the lightning strikes near you; produced by the gathering of the lightning from as many points of the cloud where it was diffused, to unite in one current and produce the “clap” or “peal”—and to the “pouring” of the rain, which follows the union of the vesicles, after the excess of repelling electricity is discharged.
Nochangeof temperature is observed when fogs form, except the ordinary change between night and day; and it seems perfectly obvious, in looking at all the phenomena, that fogs form at a temperature of 70° or 75°, in consequence of the electric influence of the earth upon the adjoining surface-atmosphere; and, when formed, they withstand the most intense action of a summer sun, till the time of day arrives for the barometric and electric tension to fall, condensation to take place in the counter-trade above, and wind to be induced. Who that has noticed the almost blistering force of the solar rays, as they break through a section of high fog, about 10A.M., can forget them.
Fogs form near the earth, during the night, when the atmosphere above is loaded with moisture manydegrees colder, and yet remains free from condensation. On the other hand, during the heat of the day, and of the hottest days, the heavy rains condense above—nay, they frequently fall at a temperature of 75° to 80°, in the tropics, and of 50° to 55° in mid-winter here.
Thus far, an adherence to the opinion that condensation was simply a cooling process; the driving out of its latent heat, not merely to another body to make an equilibrium, but “getting rid of it” by positive active radiation, or in some other way, so as to cool off and condense, has involved the formation and classification of clouds in obscurity. Hopkins (Atmospheric Changes, p. 331) laments this, but fettered by a false and imperfect theory, in relation to the tension of vapor, he falls into a similar error.
Now, there are, as we have seen, peculiar, distinctly-marked varieties of cloud, connected with peculiar and distinctly-marked conditions of the atmosphere,irrespective of temperature. None of the theories advanced, account, or profess to account for the differences in either. No modification of the calorific theory will account for them. They differ in shape, in color, in tendency to precipitation, in line of progress, and in electrical character. The explanation of this is found in the fact, that they form in distinct and different strata, partake of the positive electric character of the one, or the negative of the other; or are secondary, induced by the action of a primary condensation in a different stratum. There is not any mingling of the different strata, as has been supposed; and many other facts than those to which wehave alluded, show that the formation of cloud is a magneto-electric process.
The observations of Reid show that every violent shower cloud has the electricities disturbed, and portions of it are positive, and others negative. Howard gives us the followingrésuméof Reid’s observations:
“From an attentive examination of Reid’s observations I have been able to deduce the following general results:“1.The positive electricity, common to fair weather, often yields to a negative state before rain.“2.In general, the rain that first falls, after a depression of the barometer, isNEGATIVE.“3.Above forty cases of rain, in one hundred, give negativeelectricity; although the state of the atmosphere is positive, before and afterward.“4.Positive rain, in a positive atmosphere, occurs more rarely: perhaps fifteen times in one hundred.“5.Snow and hail, unmixed with rain, are positive, almost without exception.“6.Nearly forty cases of rain, in one hundred, affected the apparatus with both kindsof electricity; sometimes with an interval, in which no rain fell; and so, that a positive shower was succeeded by a negative; and,vice versâ; at others, the two kinds alternately took place during the same shower; and, it should seem,with a space of non-electric rain between them.”
“From an attentive examination of Reid’s observations I have been able to deduce the following general results:
“1.The positive electricity, common to fair weather, often yields to a negative state before rain.
“2.In general, the rain that first falls, after a depression of the barometer, isNEGATIVE.
“3.Above forty cases of rain, in one hundred, give negativeelectricity; although the state of the atmosphere is positive, before and afterward.
“4.Positive rain, in a positive atmosphere, occurs more rarely: perhaps fifteen times in one hundred.
“5.Snow and hail, unmixed with rain, are positive, almost without exception.
“6.Nearly forty cases of rain, in one hundred, affected the apparatus with both kindsof electricity; sometimes with an interval, in which no rain fell; and so, that a positive shower was succeeded by a negative; and,vice versâ; at others, the two kinds alternately took place during the same shower; and, it should seem,with a space of non-electric rain between them.”
Howard attributes, with great apparent probability, the successive differences in the electrical character of the rain, to the passage of different portions of the cloud, having different polarity, over the place of observation. Sopositive hail, andnegative rainfall inparallel bandsfrom the same cloud. Many such instances are on record. It should be remembered that he is describing the phenomena in the showery climate of England.
But the most decisive, perhaps, as well as practically important evidence of the influence of magnetism, or magneto-electricity, in meteorological phenomena, isderived from the action of storms. My observation has been limited, for my life has been, and must be, a practical one. But, subject to future, and I hope speedy corroboration, or correction, by extensive systematic observation, I think I may venture to divide all storms into four kinds:
1. Those which come to us from the tropics, and constitute the class investigated by Mr. Redfield. That these are of a magneto-electric character is evident. They originate near the line of magnetic intensity, over, or in the vicinity of, the volcanic islands of the tropics; are largely accompanied by electrical phenomena; extend laterally as they progress north; induce and create a change of temperature in advance of them, and do not abate until they pass off over the Atlantic to the E. or N. E., and perhaps not until they reach the Arctic circle. Their extensive and continued action is not owing to any meremechanical agencyof the adjoining passive air, or other supposed currents, originated, no man can tell how, but they concentrate upon themselves the local magnetic currents as they pass over and intersect them, and, by their inductive action upon the surface-atmosphere, in different directions, attract it under them, and within their more active influence. Here the action of the magnetic currents is probably the primary cause, but the power of the storm to concentrate upon itself the new magnetic currents which it intersects as it enters each new, successive field, enables them to maintain and extend their action.
The following diagram illustrates the course andgradual enlargement of a mid-autumn tropical storm, which induces a S. E. wind in front, and occasions a thaw.
Fig. 20.
2. Another class originate at the N. W., and extend gradually south easterly on the magnetic meridian. These are most frequent in summer, forming belts of showers, but occur, I believe, at all seasons of the year. They seem to be produced by magnetic waves passing south, and are followed in autumn and winter, and sometimes in summer, by the peculiar N. W. wind and scud, and a term of cooler weather.
Thus, it is believed that many, perhaps all of the alternating terms of heat and cold, are dependent on magnetic waves passing over the country in a similar manner, with a greater or less belt of condensation between them, and depending on peculiar magneticaction traveling in the same way. The S. E. extension of showers and storms, and the cooler changes of temperature which immediately follow them; with light N. W. wind in mid-summer, and with it fresher at earlier and later periods, in the form of northers blowing violently, according to the season, are intimately connected, and indicate such waves. The indication is strengthened also by the frequent progress of auroras in like manner, occurring usually after the belt of condensation has passed, and frequently following it. The clouds and currents of the atmosphere, so far as I have been able to discover, show no permanent current from the pole to the atmospheric equator, compensating for the counter-trade; and that compensation is furnished by the periodical but frequent atmospheric waves, connected with the periodical changes of storm, and cloud, and sunshine, which gradually extend from north to south, in or near the magnetic meridian. Perhaps such compensating currents are found west of the magnetic poles, as we have suggested, and make the N. E. and northerly dry winds of Western Europe and the Pacific; but, in the present state of our knowledge, it is impossible to say that they are. If it be so, the compensation they furnish must be small; for the volume of counter-trade which is not depolarized before it reaches the Arctic circle, and which passes round the magnetic pole, must be very small. A majority of our periodical changes, during the northern transit, and I believe at all seasons, are of this character; and, I have reason to believe, from observation, inone or two cases, that where belts of rains and showers begin, overany localityin the United States, they may assume this character. I have been in Saratoga when an easterly storm commencedsouth of that place; the condensation and mackerel sky being visible at the south, and no cloud formation or rain occurring there at the time, and have traced it afterward as a belt which had a lateral extension south-eastward. Leaving that place immediately after a belt had passed south, I have overtaken it by railroad, and run into it again before arriving at New York; and witnessed its subsequent extension south-eastwardly, out over the Atlantic. I have witnessed the approach of such a belt in the spring, at Sandusky, upon Lake Erie, and its passage over to the S. E., followed by the N. W. wind, as Mr. Bassnett describes them at Ottawa, and run under the attenuated edge of the same belt, on the same day, on the way to Pittsburg, leaving the N. W. wind behind, but finding it present again with clear sky on the following morning. I have seen hundreds of them approach from the north, and pass to S. E., out over the Atlantic; followed by the N. W. wind in spring and autumn. This class of storms pass off toward, and doubtless over the track, of our European steamers and packets. I know this, for I witness it nearly every month in the year. It is not a matter of speculation, but of actual, long-continued observation. Probably, as one approaches the Gulf Stream, and when over it, its induced winds may be more violent. It is time our navigators understood this; and that all the gales of the North Atlantic, certainly, are notrotary; and do not approach from the S. W. in the same manner as the class investigated by Mr. Redfield do. Where a fresh southerly or south-westerly wind is followed by any considerable cirro-stratus or stratus-condensation, it is usually of this character.
The following diagram exhibits the peculiarities of this class of storms. It is intended to represent the same storm or belt of showers, ontwo successivedays, and, of course, its usual rate of southerly extension:
Fig. 21.
This class of storms, or belts of showers, present the following succession of phenomena in summer:
1. Still warm weather, one or more days.
2. Fresh southerly wind, one or more days; if more than one, dying away at the S. W., at night-fall, but continuing into the evening of the day before the belt of condensation arrives.
3. Belt of condensation, with or without rain orshowers, with the easterly wind blowing axially, if the condensation is heavy and the belt wide; westerly if the condensation is feeble or the belt narrow—the clouds moving about E. N. E.
4. Cooler air, light N. W. in summer, heavy N. W. in autumn, winter, and spring.
And, the next period—
5. Still warm weather or light airs.
6. Southerly wind, fresh.
7. Belt of condensation.
8. Cool northerly wind.
And so on, successively, unless broken in upon by some other class.
Sometimes these periods are exceedingly regular, at other times the other classes prevail. I have much reason to believe that this is thenormal, periodicprovision for condensation of our portion of the northern hemisphere, and probably of every other where rain falls regularly in the summer season, and that the other classes are exceptions, as the hurricanes are exceptions to the normal condition of the weather every where. Perhaps in some seasons, during the northern transit, the exceptions may equal the rule, but I do not now remember such a season. In other years nearly all the storms are of this character. Thus, Dr. Hildreth (in Silliman’s Journal for 1827), speaking of the year 1826, in a note to his register of that year, says: “There have been, this year, an unusual number of winds from N. or N. W. Nearly every rain the past summer has been followed with winds from the northward, when, in many previous summers, the wind continued to the southward afterrain.” The immediate occurrence of northerly wind after the passage of the belt of condensation, is a peculiar feature of this class of storms.
As this also will be new, and is of great practical interest, I shall be pardoned for referring to other evidence. Bermuda is in latitude 32° north. In the summer season they are within the range of the Calms of Cancer, as Lieutenant Maury terms them, and not subject to storms. From November to May, inclusive, they have successions of revolving wind. Colonel Reid gave them much attention, and studied them barometrically: that is, he studied the changes of the wind during the successive periodic depressions. He found them revolving like ours, and hence inferred the truth of the gyratory theory in relation to all winds. But it is perfectly evident the same polar belts which pass over us reach them during the southern transit. The precedent southerly wind, thecentral condensation, the appearance of lightning, and the rotation of the wind by both the east and west, but most frequently by west, are the same. In his chapter on observations at the Bermudas, he gives us many examples. Probably the existence of the Gulf Stream to the west and north has a modifying influence upon them, and their action becomes less intense in that latitude, but they are very similar. I copy a record of the weather, for a month, which may be found on pages 252, 253, and 254, and a portion of his remarks:
“The month of December, 1839, presents a continual succession of revolving winds passing over the Bermudas, with scarcely anirregularity, as regards the fall and rise of the barometer accompanying the veering of the wind. One, however, occurred on the 10th and 11th. The S. W. wind abated, and changed to W. N. W., with the barometer still falling. But in the column of remarks it is noted that there was lightning seen in the N. and N. W., from 7P.M., during the night. This irregularity may, therefore, have been occasioned by a gale passing over the banks of Newfoundland, influencing the direction of the wind at Bermuda.
“The month of December, 1839, presents a continual succession of revolving winds passing over the Bermudas, with scarcely anirregularity, as regards the fall and rise of the barometer accompanying the veering of the wind. One, however, occurred on the 10th and 11th. The S. W. wind abated, and changed to W. N. W., with the barometer still falling. But in the column of remarks it is noted that there was lightning seen in the N. and N. W., from 7P.M., during the night. This irregularity may, therefore, have been occasioned by a gale passing over the banks of Newfoundland, influencing the direction of the wind at Bermuda.
“REVOLVING WINDS.
“Remark printed in the Register.“The changes of the wind during the December gales have been nearly the same in all:i. e., commencing with a southerly wind at first, the wind has veered by the west, toward the north-west, sometimes ending as far round as N. N. W.”
“Remark printed in the Register.
“The changes of the wind during the December gales have been nearly the same in all:i. e., commencing with a southerly wind at first, the wind has veered by the west, toward the north-west, sometimes ending as far round as N. N. W.”
These extracts show the passage of several successive belts, each with the phenomena in regular order.
The first commences with blue sky and detached clouds, barometer up, thermometer down to 65°, and nearly calm, on the 30th of November.
Dec. 1 (at noon). Wind freshens from S. S. W.; thermometer rises; barometer still up.
Dec. 2. Barometer has fallen; thermometer up; wind increasing from S. W., with gloomy, squally appearance.
Dec. 3. Wind S. S. W.; barometer slowly falling; thermometer slightly.
Dec. 4. Wind fresh; S. W.; condensation and rain has reached them, and it carries barometer and thermometer down.
Dec. 5. Wind shifting by the west, and squally.
Dec. 6. Winds gets N. W.; blows fresh; barometer at its minimum, probably at the time of the change of wind, although the register does not show the precise time.
Dec. 7. Wind N. N. W.; blue sky and detached clouds (N. W. scud), cleared off; barometer elevated by the N. W. wind, from 29.55 to 29.78. Midnight: blue sky; detached clouds (N. W. scud probably); barometer up to 29.89; thermometer fallen, from the cooler character of the northerly wind.
Dec. 8. Wind having lulled as a northerly wind has got round to S. W. again; thermometer up; barometer falling, and another belt approaching, and so on.
The first and last part of December show each two regular occurrences of substantially the same phenomena. The middle is somewhat more irregular.
There were five distinctly-marked periods, and one squally, long-continued period, with a slight tendency to condensation, and a slight fall of barometer and rain on the 19th (N. W. squall probably), but not sufficient to reverse the wind to the south. In Colonel Reid’s opinion there were five revolving gales which passed over Bermuda during the month. In my opinion, there were five perfect polar waves of condensation, and one imperfect one, with as many successive southerly winds preceding the condensation, with or without rain in the center, followed by as many cold N. W. or N. N. W. winds, with squalls, in the rear, about five days apart. (Seethe * in the barometric column.)
We are at issue.Let the question be determined byactual observation, and not byspeculation. It is of fundamental and exceeding importance to the science.
Now, let us take a month in summer, from the observations of Mr. Bassnett, at Ottawa. Here the climate differs somewhat from that east of the Alleghanies; the magnetic intensity is greater, and the action more violent and irregular. That part of the country, it should be remembered, has a greater fall of rain in summer, for reasons we have stated, and those periodic revolutions are more frequent.