“1. All the magnetic elements of any place on the earth may be deduced from the thermal elements of the same; and all the great features of the distribution of the earth’s magnetism may be theoretically derived from certain prominent features in the distribution of its heat.“2. Of the magnetic elements, the horizontal intensity is nearlyproportional to the mean temperature, as measured by Fahrenheit’s thermometer; the vertical intensity is nearly proportional to the difference between the mean temperatures, at two points situated at equal distances north and south of the place, in a direction perpendicular to the iso-geothermal line; and, in general, the direction of the needle is nearly at right angles to the iso-geothermal line, while the precise course of the inflected line to which it is perpendicular may be deduced from Brewster’s formula for the temperature, by differentiating and putting the differential equal to zero.“3. As a consequence, the laws of the terrestrial distribution of the physical principles of magnetism and heat must be the same, or nearly the same; and these principles themselves must have, toward one another, the most intimate physical relations.”
“1. All the magnetic elements of any place on the earth may be deduced from the thermal elements of the same; and all the great features of the distribution of the earth’s magnetism may be theoretically derived from certain prominent features in the distribution of its heat.
“2. Of the magnetic elements, the horizontal intensity is nearlyproportional to the mean temperature, as measured by Fahrenheit’s thermometer; the vertical intensity is nearly proportional to the difference between the mean temperatures, at two points situated at equal distances north and south of the place, in a direction perpendicular to the iso-geothermal line; and, in general, the direction of the needle is nearly at right angles to the iso-geothermal line, while the precise course of the inflected line to which it is perpendicular may be deduced from Brewster’s formula for the temperature, by differentiating and putting the differential equal to zero.
“3. As a consequence, the laws of the terrestrial distribution of the physical principles of magnetism and heat must be the same, or nearly the same; and these principles themselves must have, toward one another, the most intimate physical relations.”
The magnetic elements, of which Professor Norton speaks, are the declination, dip, and horizontal and vertical forces or intensities.
I have said, that toward the areas of greatest magnetic intensity, the needle every where declines. So as intensity increases, from the magnetic equator toward the poles, the needle, when so suspended as to permit of the motion,dips, inclines downward, and the dip is greatest, on the same parallel, where intensity is greatest. To my mind, the magnetic elementsarevery intelligible. They are all attributable to attraction, and attraction is greatest where intensity is greatest. There is nothing in the earth or atmosphere to make the needle point northerly rather than in any other direction, except magnetic intensity. Thus, the greater intensity of magnetism near the northern and southern points of the globe, attracts the corresponding ends of the needle in those directions. And, as magnetism increases in quantity or intensity, and the poles are approached, the attraction increases, and the needle dips moreand more, till the focus of intensity and attraction is reached, and then it becomes perpendicular. So magnetism is unequally diffused, meridionally, in or over the earth, and there are two equidistant areas where its quantity or intensity is greatest. These exert a lateral attraction upon the needle; it yields to this attraction, and hence its declination. If it is carried on to one area of intensity, and to the center of it, it will point to the northern focus of intensity or magnetic pole; and, if carried a trifle further west, it will yield to an eastern attraction, and point directly north. If carried still further west, its declinationeastwill increase. Thus its normal direction is to the pole, on the central focus of intensity, and when it points directly north it is west of the central line of intensity. And thus, it seems to me, all the magnetic elements may be resolved into the one element of attraction by excess of intensity or activity.
This impression is strengthened by the fact that the needle moves to the east in the morning, when the solar rays increase magnetic activity in that direction, and west again, as their influence increases there.
Now, these elements—the declination and horizontal and vertical forces—all these periodical, regular, and irregular variations of magnetic activity, are intimately connected with the variations of atmospheric condition:
First, They show an increase of activity during certain hours of the day, corresponding to, and obviously connected with, the diurnal atmospheric changes.
Second, They show an increase of activity during the northern transit of the atmospheric machinery—anannualvariation.
Third, They show an increase in that activity during the latter portion of each decennial period, conforming to the occurrence of solar spots.
And, fourth,Irregular variationsof activity, corresponding with theirregular changesof atmospheric condition.
We will examine these results, and in doing so, take those of the element of declination—one answering for all.
The magnetic needle moves to the west in summer, from about 8A.M.till about 2P.M., and the extent of its progress, during that period, constitutes the magnitude of its daily variation. It is found that this variation differs in different months, and that it is normally greatest in the summer months, and least in the winter, in the ratio of about two to one. It is further found, that in different years the maximum activity occurs in different months, and that the years differ also, and there is a distinctly marked decennial period, corresponding most remarkably with the decennial maxima of recurring solar spots, as observed by Schwabe. Dr. Lamont, of Munich, gives us the following table of magnitude of declination there, for the ten years preceding 1851, which clearly exhibits this fact, and also the greater intensity during the northern transit of the atmospheric machinery. He says:
“The magnitude of the variations of declination have a period of ten years. For five years there is a uniform increase, and during the following five years a uniform decrease in the variations. With us the magnetic declination is a minimum at about eight o’clock in the morning, and is greatest at two o’clock in the afternoon. Subtracting the declination at eight o’clock from that at two o’clock, we obtainthe magnitude of the diurnal motion. From the hourly observations, conducted in this observatory since the month of August, 1840, we ascertain the following to be the magnitude of the diurnal motion for each month separately.”
“The magnitude of the variations of declination have a period of ten years. For five years there is a uniform increase, and during the following five years a uniform decrease in the variations. With us the magnetic declination is a minimum at about eight o’clock in the morning, and is greatest at two o’clock in the afternoon. Subtracting the declination at eight o’clock from that at two o’clock, we obtainthe magnitude of the diurnal motion. From the hourly observations, conducted in this observatory since the month of August, 1840, we ascertain the following to be the magnitude of the diurnal motion for each month separately.”
The Philadelphia and Toronto observations disclose the same state of facts.
Dr. Lamont, also, in his article, gives us the following table of the magnitude of the variations derived from observations at Gottingen:
A comparison of these tables, and particularly the latter, with Schwabe’s table of spots, is interesting.There is obviously a greater mean variation when the spots are most numerous. Comparing the two with the tables of Hildreth, in relation to the temperature, from 1830 to 1840, there is, to say the least, a most remarkable coincidence. And there are others equally remarkable.
There are also irregularities of action disclosed by all, in different months of the different years, and of the same year, which are obviously connected with the difference of the seasons; and there are constantly occurring irregularities and disturbances which correspond with the, as constantly occurring, irregular atmospheric phenomena. A wide field is here opened for investigation and research. I have not time or opportunity to pursue it. Enough appears, so far as I have examined, to confirm the belief that magnetism is actively concerned in the production of the varied changes, as well as the normal conditions of the weather.
In what manner does it act? An answer to this requires an extension of the inquiry. The lines of magnetic force are every instant passing upward from the earth,aroundandthroughus. Their connection with heat is unquestionable. They are intimately associated, also, with another equally obvious and intensely active agent—electricity. We speak of this as an independent, imponderable, elementary body, but how little we yet know of it. It is every where, in every thing, easily excited into action, and then traceable to a certain, but limited extent. It is set in motion, and becomes obvious to us, by thechemical action of the acids and metals of a galvanic apparatus. We separate it from the atmosphere by friction and excitation, upon non-conductors, as in the electric machine; by the cleavage of crystals and other exciting operations. We obtain it from magnets, by the magneto-electric machine, and from the lines of magnetic force which are ever passing into the atmosphere from the earth, by intersecting them with a movable iron wire, properly insulated.From the current of magnetism which has passed through us from the earth, electricity may thus be separated and collected over our heads.We set it in motion, and obtain itby heatingdifferent metals in connection, or the same metal unequally; and from certain animals—like the torpedo and the gymnotus—whose organization is such as to enable them to evolve it. In all these cases, and they constitute an epitome of the principal methods by which we obtain it in a distinct form, it is made to flow in currents. When thus obtained, and imprisoned in non-conductors, it may be discharged, and with somewhat different effect, as it is discharged in a mass, disruptively, as it is called, as from the clouds in lightning, or permitted to flow convectively, in currents, along the wires of a galvanic apparatus, or in heated air, as from the earth to a cloud in the tornado.
It is, moreover, capable of division into positive and negative, and when concentrated or disturbed in one body, it tends to create a similar disturbance or division in a contiguous mass. To this action of electricity, the term static induction is applied. Thus,a positively electrified bodyinducesa division of the electricity in a contiguous body, if both are insulated or surrounded by a non-conducting medium; the negative electricity of the contiguous body being attracted by, and tending to pass to, the positive of the adjoining body, and the positive being repelled to the opposite side. That, in its turn, if sufficiently powerful, tends to disturb the electricity of its neighbor, and attract away its negative electricity; or, if the body which contains it is free to move, to attract that. Thus, by the conflicting action of a positive atmosphere, and a negative earth, and perhaps counter-trade, influenced by magnetism and the solar rays, the currents and winds of the atmosphere are produced, the atmosphere moving with exceeding ease and rapidity. Electricity, excited into currents, or obtained and discharged in either of the methods enumerated, is identical in character, and produces certain well-known effects:
1st. Physiological.—Shocking and convulsing the animal system; producing a peculiar sensation on the tongue, and a flash before the eyes, and in sufficient quantity destroying life.
2d. Magnetic.—Deflecting the needle, and, by a suitable arrangement of wire into helices,conferring magnetic power, or constituting magnets.
3d. Luminous.—Producing light—by a spark, as it does in natural phenomena—by the glow, the brush discharge, the ball of flame, the flash, or the chain of lightning, and probably the aurora.
4th. Evolving heat.—Melting metallic substancesby concentration, with a great intensity of heat—as the wire of the galvanic apparatus, and as is sometimes seen in the effects of lightning in fusing metals on persons stricken; and setting combustibles on fire.
5th. Attraction and repulsion.—Attraction, when the currents flow parallel with each other, or are of opposite natures, and repelling when of like character.
6th. Induction.—Inducing attendant circular or other secondary currents, such as may be seen in the atmosphere during its most violent displays of active energy.
7th. Capable of being dissipated by heated air, or carried off by moisture, although isolated by dry air, of ordinary temperature, which is a bad conductor.
Now, although magnetism can not be collected, imprisoned, or discharged, like electricity, or collected at all, but by its adherence to some substance capable of magnetization, it is obvious there is an intimate association, at least, between it and electricity.They are never found alone.Allelectricitywillmagnetize. Allmagnetismwill evolve electricity. Allcurrentsofelectricityhaveencircling currentsofmagnetism, and all deflect the magnetic needle. All magnetic currents give out to intersecting wires,currents of electricity, and all magnetsinducethem.
Electricity, therefore, whether identical in substance with magnetism, but differing in form, or whether merely associated with it, as is variously believed, should be present with magnetism in greater quantity or intensity where magnetism is most intense, and active, and whenever present, should beactive and influential. And so we find, from observation, the fact to be. No inconsiderable effort has been made by the advocates of the caloric and mechanical theories, to ignore the agency of electricity and of magnetism, in the production of the varied meteorological phenomena. But it will not do. The phenomena, grouped and analyzed, disclose a potential-controlling, magneto-electric agency, and meteorology will advance rapidly to perfection, as a simple, intelligible, and practical science,as soon as that agency is admitted.
Electricity is always perceptibly present in storms and showers within the tropics. Most of the rain, from the tropical belt, falls from “thunder showers.” So hurricanes and typhoons, and all tropical storms, are confessedly, and in proportion to their intensity, “highly electric.” This excess of quantity or activity of electricity, exists in connection with the movable atmospheric machinery. When it moves up north in summer, and arrives at its highest point of northern transit,stormsare veryuncommon, and the tropical forms of cloud and showers, with thunder and lightning, prevail. This is most obvious, if not most influential, where the magnetic intensity is greatest. Violent showers, and gusts, and tornadoes, are more frequent in this country than in Europe; and over the area of greatest intensity, as in Ohio, than at a distance on the extreme eastern or western coast. And the same is true over the intense magnetic area of Asia.
Electricity, too, like magnetism, has its diurnal,and doubtless its annual and decennial variations, and also its irregular ones, and they are most obviously and intimately connected. Magnetism and electricity together, constitute the aurora. Its culmination is in the magnetic meridian—it affects the telegraph wires—is connected with the irregular disturbances which affect the magnetic needle, and does not exist in the limits of the trades, although occasionally seen from thence, when it passes south, and near them.
The aurora sometimes extends south in waves, as do the magneto-electric, atmospheric, periodical changes of cold and heat, and storm, and sunshine.The aurora is connected with the formation of cloud, and with a smoky atmosphere, similar to that with which we are familiar in summer and autumn. Thus Humboldt (Cosmos, vol. i. pp. 191, 192).
“This connection of the polar light with the most delicate cirrus clouds, deserves special attention, because it shows that the electro-magnetic evolution of light is a part of a meteorological process. Terrestrial magnetism here manifests its influence on the atmosphere, and on the condensation of aqueous vapor. The fleecy clouds seen in Iceland, by Thienemann, and which he considered to be the northern light, have been seen in recent times by Franklin and Richardson, near the American north pole, and by Admiral Wrangel on the Siberian coast of the Polar Sea. All remarked ‘that the aurora flashed forth in the most vivid beams when masses of cirrus-strata were hovering in the upper regions of the air, and when these were so thin that their presence couldonly be recognized by the formation of a halo round the moon.’ These clouds sometimes range themselves, even by day, in a similar manner to the beams of the aurora, and then disturb the course of the magnetic needle in the same manner as the latter. On the morning after every distinct nocturnal aurora, the same superimposed strata of clouds have still been observed that had previously been luminous. The apparently converging polar zones (streaks of clouds in the direction of the magnetic meridian), which constantly occupied my attention during my journeys on the elevated plateaux of Mexico, and in northern Asia, belong, probably, to the same group of diurnal phenomena.”
Mr. William Stevenson gives us (in the London, Edinburgh, and Dublin Philosophical Magazine for July, 1853) an interesting article on the connection between aurora and clouds. His observations on this most important branch of the subject trace a connection between the aurora and the formation of cloud, and open up, as he says, “a most interesting field for observation which promises to lead to very important results.” Such observations point with great significance, to the primary influence of the magneto-electricity of the earth.
To the difference in the magnetic intensity of the eastern portion of this continent, compared with Europe and our western coast, very much of the difference of climate, so far as temperature is involved, may be attributed. We have seen in what manner the iso-thermal lines surround these areas of intensity.So the most excessive climate—that is, the climate where the greatest extremes alternate, other things being equal, is upon or near the line or area of greatest magnetic intensity. I say other things being equal, because large bodies of water modify climates by equalizing the seasons—making the summers cooler and the winters warmer than the mean of the parallel.
Thus, our great interior lakes modify the climate in relation to temperature in their vicinity. Their summers are cooler and their winters warmer; but westward of them the same line of equal summer temperature, or iso-thermalline, rises with considerable abruptness, and the winter, or iso-cheimal line of equal temperature, falls in a similar manner. Thus, the range of the thermometer, from the highest elevation to the lowest depression, for the year, is very great, while in the tropics the range is comparatively small. From observations made at the military posts of the United States, Dr. Forrey deduced summer and winter lines of equal temperature, starting from the vicinity of Boston and running west, which showed most remarkably the rise of the summer lines as intensity increased, and the fall of the winter lines in like manner.
The influence of the lakes was also most obvious. The elevation of the earth increases, going west, to about 700 feet at the surface of the lakes, and to nearly 4,000 feet at the eastern base of the Rocky Mountains; and, although temperature does not decrease to as great a degree when the elevationabove the level of the sea isgradual, yet some allowance should doubtless be made for that elevation on this line. When that allowance is made, the ascent of the summer line, to the north, over the area of greatest intensity, is strikingly apparent.
Dr. Forrey also instituted a comparison between Fort Snelling, where the climate is as excessive, and the range of the thermometer as great, as in any portion of the continent in the same latitude, with Key West, and I copy his diagram. It is very instructive, showing the gradual mean rise of the temperature, from January to December, inclusive, while the cross lines show theextremes of each month.
Perhaps the most interesting part of it, is the illustration of the monthly extremes, and the contrast between them, in the excessive climate of Fort Snelling, and the tropical one of Key West. Each is a type of the climate in which it is situated. The annual range and monthly extremes are small in tropical countries, and large in extra-tropical ones. The extreme range, or greatest elevation of heat, contrary to what is generally supposed, is greater at Fort Snelling than at Key West. But the climate of the latter is modified by the adjoining ocean.
I copy, also, a table (p. 304), showing the range of the thermometer for the year, and the maxima and minima, during each month, at several other places in this country, and at London and Rome, for the purpose of showing the extent of the ranges compared with those places; and also, that these great changes in each month occur very uniformly all over the country, and may always be expected, and with considerable regularity. They are incident to our climate. I wish I could engrave the foregoing diagram, and the following table, upon the mind of every man, woman, and child in the country; and under it, in ever-visible letters, these words of precaution:Conform to the peculiarities of your climate, and clothe yourselves, at all times, in accordance with the alternations of the weather.If heeded, they would save thousands, every year, from premature death.
Fig. 18.
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The effect of this difference of magnetic intensity upon the climate of Europe is marked. There, the excessive summer heat, which our greater magnetic intensity and larger volume of counter trade give us, is unknown. Hence, while we can grow Indian corn (which requires the excessive summer heat) over all the Eastern States, up to 45°, and in some localities east of the lakes to 47° 30′, and to 50° west of them, to the base of the Rocky Mountains, and notwithstanding the increase of elevation, they can not grow it except over a limited area, and with limited success. Nor can they, or the inhabitants of any other country except China, grow profitably the kind of cotton which is so successfully grown in the Southern States of the Union. Nor can China do so to a considerable extent, because of the mountainous character of the surface. To a level and remarkably watered country, greater magnetic and electric intensity, and a greater volume of counter-trade, we are, and ever shall remain, indebted, for an almost exclusive monopoly in the growth of two of the most important staple productions of the earth. On the other hand, although the same magnetic intensity, and its winter excess of positive electricity and cold, make our winters extreme, there are but few of the productions of temperate latitudes which we can not grow successfully, and they are comparatively unimportant.
This excess of magnetic intensity and electricity not only gives a peculiar character to our vegetation, but also to our race, our animals, and every thing. He who supposes that the restless activity and energy of the people of the United States is the result of habit, or education, or any fortuitous circumstances alone, is mistaken. Let him watch the contrast in his own feelings during those occasional languid, damp, and sultry, although not thermometrically, hot days—which so much resemble the summer weather of England—with those days of bright, bracing, N. W. and S. W. air, so much more frequent here, and he will appreciate the difference. That term “bracing,” so much in use, will express the effect of this peculiar weather. It “girds up the loins,” both of body and mind. Men and animals can work with more ease, even in our peculiar extremes of heat, than they can in England, and fatten with less.
A similar difference in degree is found between our climate and that of the Pacific portion of our country. Something is due to the difference in the volume and moisture of the counter-trades, and something to the contiguity of the Pacific Ocean; but to thedifference in magneto-electric intensity, the contrast is mainly due. Corn and cotton will be grown, to some extent, in the valleys west of the meridian of 105°, but never as successfully as east of it.
The aurora is periodical, like all the other atmospheric phenomena, but its periodicity is not accurately ascertained. It is believed to have occurred much oftener during the second quarter of this century, than during the first. It is known, however, to occur most frequently in the spring and fall; and during those periods when the active and rapid transit of the atmospheric machinery produces the greatest degree of magnetic disturbance. This identifies it with terrestrial magnetism. Dalton gives us the following table of observations, arranged according to the months when they were seen.
(1) contains those observed by him at Kendall; (2) are taken from another list; (3) isMarian’slist of those observed before 1732; and (4), those seen in the State of New York in 1828 and 1830.
Mr. Stevenson’s table of those observed by him at Dunse, from 1838 to 1847, inclusive, is as follows:
Observations in this country correspond substantially with the foregoing. They are, however, seen here in the summer months more frequently than in Europe. See an article by Mr. Herrick (American Journal of Science, vol. 33. p. 297). In this, also, they conform to our greater magnetic intensity and more excessive climate.
The auroras appear to follow the polar belts of condensation and precipitation. Dalton considers them indications of fair weather. They are often most brilliant just after a storm has passed, but their continuance is no indication that another will not follow within the usual period.
The condensation with which the aurora is connected, is not, in my judgment, often in the counter-trade, or below it, but above, where feeble condensation has been seen by aeronauts when invisible at the surface of the earth. Neither the height of this condensation, not that of the aurora, have been satisfactorily ascertained. The aurora of April 7th, 1847, was a favorable one for observation. It was carefully and attentively watched by Professor Olmsted, Mr. Herrick, Dr. Ellsworth, and others, and they are intelligent and skillful observers.[9]But the nature of the aurora forbids reliance on parallax, or measurements founded on the time when, any portion of the bow or arch rises in range of a particular star. The bow or arch moves southwardly, but the same rays or currents do not. The wave of magneticactivitymoves south, and each successive current, as it is reached by theimpulse, becomes luminous.Hence the observers, when distant, do not see, at the same time, or at different times, the same rays. The phenomenon is unquestionably magneto-electric. Electricity becomes luminous in a vacuum, and De la Rive, by combining the electric currents with those of magnetism, produced all the peculiarities of the aurora. The magnetic currents, passing from the earth, have associated electric ones in connection, and these, in the upper attenuated atmosphere, become luminous. Whether, as De La Rive supposes, by combining with the positive electricity existing there, or because the associated electric currents arethenin excess, not being intercepted by atmospheric vapor and returned to the earth in rain, we can not know, nor is it very important we should.
Having thus taken a general view of the nature of magnetism and its associated electricities, and their connection with the general and obvious peculiarities of climate, let us approach more nearly the varied atmospheric phenomena, resulting from variations of pressure, temperature, condensation, and wind, and give them a closer consideration. They all have regularity and periodicity—they all occur in degree, and in connection with magnetism and electricity, during the twenty-four hours of every serene and normal summer’s day. Grouped together, in comparison with the changes in the activity and force of the magnetic elements, their connection is clearly discernible.
The day may be said, with truth, to commence, in some portion of the summer, at 4A.M.Theatmospheric does at all seasons. At that hour the barometer is at its morning minimum. It has, as we have said, a perceptible diurnal variation of two maxima and two minima. Its periods of depression are at 4A.M., and 4P.M., and of elevation at 10A.M., and 10P.M.The difference between the elevation and depression is considerable within the tropics, where Humboldt tells us the hour of the day can be known by the height of the barometer, and it decreases toward the poles. At 4A.M.it is then at one of its minima, and rises till 10 o’clock.
At, or about the same period, and sometimes when the barometer is falling, and previous thereto, there is a tendency to fog in localities subject to that condensation. This tendency is sometimes observed at the other barometric minimum, late in the afternoon or early in the evening, but less frequently. The tendency to fog condensation is greatest in this country about the morning minimum. It seems to be owing to the influence of the earth; it is confined to the surface atmosphere, and is apparently produced by the inductive agency of the negative electricity of the earth. It disappears, whether it be high or low fog, about the time when the barometer attains its morning maximum, or about 10A.M.
At about that period, when there has been fog, or earlier, when there has not, and sometimes as early as 8A.M., there is a tendency to trade condensation—cirrus in mid-winter, and a cumulus in mid-summer, and, during the intermediate time, a tendency to cirro-stratus, partaking more or less of thecharacter of one or the other, according to the season.
Temperature, in summer, commences its diurnal elevation about 4A.M., also, and rises till about 2P.M.From that time it falls with very little variation till 4 o’clock the next morning. It has but one maximum and one minimum in the twenty-four hours.
As the morning barometric maximum approaches, and the heat increases the magnetic activity, condensation in the trade appears, or induced condensation in the upper portion of the surface atmosphere, that portion near the earth is affected and attracted—and the “wind rises,” according to the locality, the season, and the activity of the condensation. The tendency to blow increases with the tendency to trade and cumulus condensation, and continues till toward night, when it gradually dies away, unless there be a storm approaching. As the heat increases, and stimulates magnetism into activity, the magnetic needle commences moving to the west, its regular diurnal variation, and continues to do so until about 2P.M., when it commences returning to the east, and so continues to return until 10P.M., when it moves west again until 2A.M., and from thence to the east, till 8A.M.
Similar variations also take place in the horizontal force, as evinced by the action of the magnetometer needle, and in the vertical force, as shown by the oscillations. So that it is evident that there are two maxima, and two minima of magnetic activity every day, shown by all the methods by which we measuremagnetic action and force—more than double at the acme of northern summer transit over that of winter, and proceedingpari passu, with the other daily phenomena—evincing the same irregular action which the other phenomena evince. Still another phenomenon, which has a daily change, is electric tension, or the increase or decrease in the tension of the positive or true atmospheric electricity.
Fig. 19.