The Philosophy of the Weather Part 20

1st. Physiological.--Shocking and convulsing the animal system; producing a peculiar sensation on the tongue, and a flash before the eyes, and in sufficient quant.i.ty destroying life.

2d. Magnetic.--_Deflecting the needle_, and, by a suitable arrangement of wire into helices, _conferring magnetic power_, or const.i.tuting 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 a.s.sociation, 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 a.s.sociated with it, as is variously believed, should be present with magnetism in greater quant.i.ty 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 a.n.a.lyzed, 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 quant.i.ty 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, const.i.tute 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 pa.s.ses 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 suns.h.i.+ne.

_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 ma.s.ses 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 inst.i.tuted 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 lat.i.tude, 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 ill.u.s.tration 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.

[Ill.u.s.tration: Fig. 18.]

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 lat.i.tudes which we can not grow successfully, and they are comparatively unimportant.

A Fort Vancouver, Oregon Territory B Fort Brady, outlet of Lake Sup.

C Hanc.o.c.k Barracks, Houlton, Me.

D Fort Armstrong, Rock Island, Ill.

E West Point, New York F Was.h.i.+ngton, 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 46 46 41 41 38 38 29 51 41 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 circ.u.mstances 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, 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 pa.s.sed, 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, pa.s.sing from the earth, have a.s.sociated 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 a.s.sociated 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 a.s.sociated 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.