Chapter X (1)

We are yet ignorant of the true nature of magnetism. We trace its lines, as in the diagrams, upon and around the magnet; but we can only do this with soft iron, or other substance, in which magnetic action may be induced. We know that these lines are currents, or lines of force, for that force produces sensible effects, and we measure it by the movements of the needle. We know that these lines may be _deflected_ by other magnetic bodies, and concentrated upon them. We know that the earth, and the smallest magnets, exhibit properties in common. The poles of the magnet are some distance from its extreme ends--so are those of the earth. The intensity increases, from the center, or near it, to the poles of the magnet, as shown by its attraction; and the same increase of magnetic intensity, from the magnetic equator to the magnetic poles, or near them, is traced upon the earth.

We know that there are two lines, or rather _areas_, of greater intensity upon the globe. One extending from the American magnetic pole, south-eastwardly, to a corresponding pole in the southern hemisphere; and another, the Asiatic, extending from the Siberian pole to a corresponding southern one, in like manner. We know that, from those lines or areas, the intensity, east and west, on the same parallel of latitude, decreases each way, to about midway between them. Thus, calling the intensity where Humboldt found the magnetic equator over South America, in 7 deg. 1' south latitude, 1, or unity--the least intensity known is, .706, found at the magnetic equator, over the South Atlantic, and at its most southern depression; and it increases to 1.4 in the West Indies, and to 2.0099 upon one or more points of the North American continent, south of the magnetic pole, and about the meridian of 92 deg.. That it is 1.805, at Warren, Ohio, in latitude 41 deg. 16', and longitude 72 deg. 57', and decreases to 1.774 at New Haven, Connecticut, in latitude 41 deg. 18'. That it is but 1.348 at Paris, nearly one third less than on the same latitude in some portions of this continent. That the line of equal intensity, or "_iso-dynamic_" line, of 1-8/10, is a closed curve of an oval shape, extending somewhat below 40 deg., in the longitude of Cincinnati, and reaches off nearly to Bhering's Straits, on the west; rising in a similar manner, though not so abruptly, on the east; including the great northern lakes and a considerable part of Hudson's Bay. While the iso-dynamic lines of 1-85/100, and 1-875/1000, are smaller ovals, included within the former. Such, at least, is the present belief from such investigations as have been made. (See an article by Professor Loomis, American Journal of Science, new series, vol. iv. p. 192.)

Our subject demands a still closer examination of the elements of magnetism and its associated electricities, and their influence upon climate and the atmosphere with a view to the solution of the questions in hand, and we will pursue the inquiry in the present chapter.

Waiving, for the present, any further notice of the fact that the counter-trades are concentrated over, and contiguous to, this area of intensity, for the purpose of examining the magnetic phenomena independently, and intending to return to a consideration of their connection with it, we observe:--That it is now well settled that the iso-geothermal lines, or lines of equal terrestrial heat, are coincident, or nearly so, with the lines of equal magnetic intensity. The points where the magnetic intensity is at a minimum, on the magnetic meridian, are the warmest points of that meridian, and those where it is most intense, the coldest.

The magnetic elements of a place may be computed from its thermal ones. The laws producing or governing the distribution of one, have an intimate physical relation with those producing or governing the other. Professor Norton ably sums up a discussion of the subject (in the American Journal of Science for September, 1847), omitting the theoretic propositions, as follows:

"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 nearly
proportional 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 elements are very 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 more and 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 declination _east_ will 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--an _annual_ variation.

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 variations_ of activity, corresponding with the _irregular changes_ of 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 8 A.M. till about 2 P.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 obtain
_the 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."

+-------------------------------------------------------------------+
| | Jan. | Feb. | March.| April.| May. | June. | July. | Aug. |
+-------------------------------------------------------------------|
| 1841 | 3.72 | 5.13 | 8.43 | 11.49 | 11.47 | 11.49 | 10.07 | 9.86|
| 1842 | 3.65 | 4.74 | 8.34 | 10.33 | 9.31 | 9.78 | 8.38 | 9.03|
| 1843 | 3.82 | 4.08 | 6.87 | 9.71 | 9.24 | 10.14 | 9.57 | 10.08|
| 1844 | 2.81 | 3.43 | 6.95 | 9.53 | 8.42 | 8.88 | 8.38 | 9.28|
| 1845 | 2.20 | 4.69 | 8.26 | 11.93 | 10.88 | 10.73 | 9.44 | 10.42|
| 1846 | 3.30 | 6.94 | 9.53 | 12.27 | 12.58 | 11.21 | 11.37 | 11.49|
| 1847 | 3.30 | 6.35 | 9.85 | 12.43 | 11.81 | 11.76 | 10.94 | 12.87|
| 1848 | 6.52 | 9.01 | 11.96 | 14.56 | 14.22 | 13.80 | 14.67 | 15.40|
| 1849 | 7.27 | 8.42 | 14.08 | 16.86 | 13.67 | 13.86 | 12.57 | 11.54|
| 1850 | 5.98 | 8.84 | 12.15 | 14.32 | 14.05 | 13.39 | 12.53 | 12.68|
+-------------------------------------------------------------------+
+----------------------------------------------------+
| Sept. | Oct. | Nov. | Dec. | Autmn | Spring| Year.|
| | | | |& Wint.| & Sum.| |
|----------------------------------------------------|
| 8.78 | 6.82 | 3.71 | 2.89 | 5.12 | 10.53 | 7.82|
| 7.72 | 7.05 | 3.86 | 2.81 | 5.07 | 9.09 | 7.03|
| 8.81 | 6.82 | 3.82 | 2.79 | 4.70 | 9.59 | 7.15|
| 8.23 | 6.54 | 3.94 | 2.98 | 4.44 | 8.79 | 6.61|
| 8.82 | 7.34 | 4.49 | 8.34 | 5.89 | 10.87 | 8.13|
| 10.39 | 7.82 | 5.66 | 3.22 | 6.08 | 11.25 | 8.81|
| 12.06 | 11.53 | 7.06 | 4.70 | 7.63 | 11.98 | 9.55|
| 14.00 | 10.30 | 5.78 | 3.53 | 7.85 | 14.44 | 11.05|
| 10.79 | 9.12 | 5.41 | 4.09 | 8.06 | 13.21 | 10.64|
| 12.64 | 9.04 | 6.20 | 3.45 | 7.61 | 13.27 | 10.44|
+----------------------------------------------------+

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:

+--------------------+
| Year.|Mean of Year.|
|--------------------|
| 1835 | 9.57 |
| 1836 | 12.34 |
| 1837 | 12.27 |
| 1838 | 12.79 |
| 1839 | 11.03 |
| 1840 | 9.91 |
| 1841 | 8.70 |
+--------------------+

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, _around_ and _through_ us. 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 the chemical 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 it _by heating_ different 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 body _induces_ a 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 substances by 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._ All _electricity_ will _magnetize_. All _magnetism_ will evolve electricity. All _currents_ of _electricity_ have _encircling currents_ of _magnetism_, and all deflect the magnetic needle. All magnetic currents give out to intersecting wires, _currents of electricity_, and all magnets _induce_ them.

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 be active 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, _storms_ are very _uncommon_, 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 could only 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-thermal line, 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 elevation above the level of the sea is _gradual_, 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 the _extremes 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.

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 deg., and in some localities east of the lakes to 47 deg. 30', and to 50 deg. 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.

A Fort Vancouver, Oregon Territory
B Fort Brady, outlet of Lake Sup.
C Hancock Barracks, Houlton, Me.
D Fort Armstrong, Rock Island, Ill.
E West Point, New York
F Washington, D. C.
G Jefferson Barracks, near St. Louis
H Fort King, interior of East Florid.
I Environs of London
K Rome, Italy

A B C D E F H I J K

Lat. 45 deg. 46 deg. 46 deg. 41 deg. 41 deg. 38 deg. 38 deg. 29 deg. 51 deg. 41 deg.
37' 39' 10' 28' 22' 53' 28' 12' 31' 54'
Annual
Range. 78 110 118 106 91 84 89 78 67 62

Jan. Min. 17 -21 -24 -10 -1 14 10 33 16 29
Max. 58 40 41 48 53 57 60 83 49 58
Feb. Min. 32 -22 -11 -6 2 16 11 43 19 33
Max. 55 44 42 56 56 62 70 84 54 60
Mar. Min. 32 -7 -1 13 16 28 31 39 24 37
Max. 60 51 54 70 72 70 76 87 60 65
Apr. Min. 32 18 24 33 40 36 38 54 26 44
Max. 70 62 74 78 62 73 83 93 69 74
May. Min. 32 32 81 44 47 50 45 64 33 52
Max. 75 79 83 84 72 85 88 97 78 80
June. Min. 45 41 38 57 57 59 59 73 39 60
Max. 95 86 90 89 79 92 95 105 80 88
July. Min. 40 39 45 62 64 64 50 73 41 64
Max. 95 84 90 95 86 94 96 102 83 91
Aug. Min. 44 49 46 60 62 63 66 72 42 62
Max. 95 84 85 91 87 93 96 104 79 91
Sept. Min. 43 40 33 51 56 51 51 70 34 55
Max. 88 75 78 87 83 88 88 99 75 85
Oct. Min. 50 27 24 82 42 33 38 41 30 46
Max. 66 70 72 73 69 77 80 91 68 77
Nov. Min. 32 15 4 26 36 28 27 30 22 39
Max. 58 58 60 64 63 66 69 82 56 67
Dec. Min. 32 -7 -4 15 20 17 14 36 20 31
Max. 55 42 53 62 56 61 64 79 53 60

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 the difference 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 deg., 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.

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.

(1) 18 18 26 32 21 5 2 21 23 36 38 9
(2) 21 18 23 13 3 2 1 3 35 22 22 21
(3) 21 27 22 12 1 5 7 9 34 50 26 15
(4) 5 6 4 8 10 7 6 14 14 17 5 6

(1) contains those observed by him at Kendall; (2) are taken from another list; (3) is MARIAN'S list 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:

Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.
32 20 18 18 3 0 2 14 43 34 30 23

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 magnetic _activity_ moves south, and each successive current, as it is reached by the _impulse_, 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 are _then_ in 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 4 A.M. The atmospheric 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 4 A.M., and 4 P.M., and of elevation at 10 A.M., and 10 P.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 4 A.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 10 A.M.

At about that period, when there has been fog, or earlier, when there has not, and sometimes as early as 8 A.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 the character of one or the other, according to the season.

Temperature, in summer, commences its diurnal elevation about 4 A.M., also, and rises till about 2 P.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 2 P.M., when it commences returning to the east, and so continues to return until 10 P.M., when it moves west again until 2 A.M., and from thence to the east, till 8 A.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 measure magnetic action and force--more than double at the acme of northern summer transit over that of winter, and proceeding _pari 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.

The following table shows the mean two hourly tensions for three years, at Kew, viz.:

Hours 12 P.M. 2 A.M. 4 A.M. 6 A.M. 8 A.M. 10 A.M.
Number of observations 655 784 804 566 1,047 1,013
Tension 22.6 20.1 20.5 34.2 68.2 88.1

Hours 12 A.M. 2 P.M. 4 P.M. 6 P.M. 8 P.M. 10 P.M.
Number of observations 848 858 878 874 878 1,007
Tension 75.4 71.5 69.1 84.8 102.4 104

From this it will be seen that the tension of electricity is at a minimum at 4 A.M., also, that it rises till 10, falls till 4 P.M., but not as rapidly, rises till 10, falls again till 4 A.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 (figure 17.)

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 of any 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:

CAUSE. | EFFECT. | EFFECT.
| |
Increase of magnetic|Decrease of pressure. |Increase of primary
or magneto-electric | |condensation.
activity, as shown |Of positive electric |
by declination and |tension. |Of wind.
increase of | |
horizontal and |Of surface condensation,|Of electrical disturbance
vertical force. |_i. e._, fog and dew. |and phenomena in the
| |trade and its vicinity.

This connection is equally obvious if the order is reversed--thus;

CAUSE. | EFFECT. | EFFECT.
| |
Decrease of magnetic|Increase of pressure. |Disappearance of primary
or magneto-electric | |condensation.
activity. |Of tension of |
|atmospheric electricity.|Of wind, and
| |
|Of surface condensation,|Of electric disturbance
|_i. e._, fog and dew. |in the trade and its
| |vicinity.

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 knowledge of 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, and its 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, in _different strata_ and 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 portion _more 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 productions of 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 deg.._ It is mainly a _summer 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 the _negative_ wire 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 thousand _crackling_ sounds 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.

No _change_ of 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 deg. or 75 deg., 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 10 A.M., can forget them.

Fogs form near the earth, during the night, when the atmosphere above is loaded with moisture many degrees 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 deg. to 80 deg., in the tropics, and of 50 deg. to 55 deg. 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 we have 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 following _resume_ of 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, is_ NEGATIVE.

"3. _Above forty cases of rain, in one hundred, give negative_
electricity; 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 kinds_ of electricity; sometimes with an
interval, in which no rain fell; and so, that a positive shower was
succeeded by a negative; and, _vice versa_; 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. So _positive hail_, and _negative rain_ fall in _parallel bands_ from 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, is derived 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: