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.
[Illustration: 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 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.
[Illustration: Fig. 19.]
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:
1. Those which come to us from the tropics, and constitute the class
investigated by Mr. Redfield. That these are of a magneto-electric
character is evident. They originate near the line of magnetic intensity,
over, or in the vicinity of, the volcanic islands of the tropics; are
largely accompanied by electrical phenomena; extend laterally as they
progress north; induce and create a change of temperature in advance of
them, and do not abate until they pass off over the Atlantic to the E. or
N. E., and perhaps not until they reach the Arctic circle. Their extensive
and continued action is not owing to any mere _mechanical agency_ of the
adjoining passive air, or other supposed currents, originated, no man can
tell how, but they concentrate upon themselves the local magnetic currents
as they pass over and intersect them, and, by their inductive action upon
the surface-atmosphere, in different directions, attract it under them,
and within their more active influence. Here the action of the magnetic
currents is probably the primary cause, but the power of the storm to
concentrate upon itself the new magnetic currents which it intersects as
it enters each new, successive field, enables them to maintain and extend
their action.
The following diagram illustrates the course and gradual enlargement of a
mid-autumn tropical storm, which induces a S. E. wind in front, and
occasions a thaw.
[Illustration: Fig. 20.]
2. Another class originate at the N. W., and extend gradually south
easterly on the magnetic meridian. These are most frequent in summer,
forming belts of showers, but occur, I believe, at all seasons of the
year. They seem to be produced by magnetic waves passing south, and are
followed in autumn and winter, and sometimes in summer, by the peculiar N.
W. wind and scud, and a term of cooler weather.
Thus, it is believed that many, perhaps all of the alternating terms of
heat and cold, are dependent on magnetic waves passing over the country in
a similar manner, with a greater or less belt of condensation between
them, and depending on peculiar magnetic action traveling in the same
way. The S. E. extension of showers and storms, and the cooler changes of
temperature which immediately follow them; with light N. W. wind in
mid-summer, and with it fresher at earlier and later periods, in the form
of northers blowing violently, according to the season, are intimately
connected, and indicate such waves. The indication is strengthened also by
the frequent progress of auroras in like manner, occurring usually after
the belt of condensation has passed, and frequently following it. The
clouds and currents of the atmosphere, so far as I have been able to
discover, show no permanent current from the pole to the atmospheric
equator, compensating for the counter-trade; and that compensation is
furnished by the periodical but frequent atmospheric waves, connected with
the periodical changes of storm, and cloud, and sunshine, which gradually
extend from north to south, in or near the magnetic meridian. Perhaps such
compensating currents are found west of the magnetic poles, as we have
suggested, and make the N. E. and northerly dry winds of Western Europe
and the Pacific; but, in the present state of our knowledge, it is
impossible to say that they are. If it be so, the compensation they
furnish must be small; for the volume of counter-trade which is not
depolarized before it reaches the Arctic circle, and which passes round
the magnetic pole, must be very small. A majority of our periodical
changes, during the northern transit, and I believe at all seasons, are of
this character; and, I have reason to believe, from observation, in one
or two cases, that where belts of rains and showers begin, over _any
locality_ in the United States, they may assume this character. I have
been in Saratoga when an easterly storm commenced _south of that place_;
the condensation and mackerel sky being visible at the south, and no cloud
formation or rain occurring there at the time, and have traced it
afterward as a belt which had a lateral extension south-eastward. Leaving
that place immediately after a belt had passed south, I have overtaken it
by railroad, and run into it again before arriving at New York; and
witnessed its subsequent extension south-eastwardly, out over the
Atlantic. I have witnessed the approach of such a belt in the spring, at
Sandusky, upon Lake Erie, and its passage over to the S. E., followed by
the N. W. wind, as Mr. Bassnett describes them at Ottawa, and run under
the attenuated edge of the same belt, on the same day, on the way to
Pittsburg, leaving the N. W. wind behind, but finding it present again
with clear sky on the following morning. I have seen hundreds of them
approach from the north, and pass to S. E., out over the Atlantic;
followed by the N. W. wind in spring and autumn. This class of storms pass
off toward, and doubtless over the track, of our European steamers and
packets. I know this, for I witness it nearly every month in the year. It
is not a matter of speculation, but of actual, long-continued observation.
Probably, as one approaches the Gulf Stream, and when over it, its induced
winds may be more violent. It is time our navigators understood this; and
that all the gales of the North Atlantic, certainly, are not rotary; and
do not approach from the S. W. in the same manner as the class
investigated by Mr. Redfield do. Where a fresh southerly or south-westerly
wind is followed by any considerable cirro-stratus or stratus-condensation,
it is usually of this character.
The following diagram exhibits the peculiarities of this class of storms.
It is intended to represent the same storm or belt of showers, on _two
successive_ days, and, of course, its usual rate of southerly extension:
[Illustration: Fig. 21.]
This class of storms, or belts of showers, present the following
succession of phenomena in summer:
1. Still warm weather, one or more days.
2. Fresh southerly wind, one or more days; if more than one, dying away at
the S. W., at night-fall, but continuing into the evening of the day
before the belt of condensation arrives.
3. Belt of condensation, with or without rain or showers, with the
easterly wind blowing axially, if the condensation is heavy and the belt
wide; westerly if the condensation is feeble or the belt narrow--the
clouds moving about E. N. E.
4. Cooler air, light N. W. in summer, heavy N. W. in autumn, winter, and
spring.
And, the next period--
5. Still warm weather or light airs.
6. Southerly wind, fresh.
7. Belt of condensation.
8. Cool northerly wind.
And so on, successively, unless broken in upon by some other class.
Sometimes these periods are exceedingly regular, at other times the other
classes prevail. I have much reason to believe that this is the _normal,
periodic_ provision for condensation of our portion of the northern
hemisphere, and probably of every other where rain falls regularly in the
summer season, and that the other classes are exceptions, as the
hurricanes are exceptions to the normal condition of the weather every
where. Perhaps in some seasons, during the northern transit, the
exceptions may equal the rule, but I do not now remember such a season. In
other years nearly all the storms are of this character. Thus, Dr.
Hildreth (in Silliman's Journal for 1827), speaking of the year 1826, in a
note to his register of that year, says: "There have been, this year, an
unusual number of winds from N. or N. W. Nearly every rain the past summer
has been followed with winds from the northward, when, in many previous
summers, the wind continued to the southward after rain." The immediate
occurrence of northerly wind after the passage of the belt of
condensation, is a peculiar feature of this class of storms.
As this also will be new, and is of great practical interest, I shall be
pardoned for referring to other evidence. Bermuda is in latitude 32 deg.
north. In the summer season they are within the range of the Calms of
Cancer, as Lieutenant Maury terms them, and not subject to storms. From
November to May, inclusive, they have successions of revolving wind.
Colonel Reid gave them much attention, and studied them barometrically:
that is, he studied the changes of the wind during the successive periodic
depressions. He found them revolving like ours, and hence inferred the
truth of the gyratory theory in relation to all winds. But it is perfectly
evident the same polar belts which pass over us reach them during the
southern transit. The precedent southerly wind, the _central
condensation_, the appearance of lightning, and the rotation of the wind
by both the east and west, but most frequently by west, are the same. In
his chapter on observations at the Bermudas, he gives us many examples.
Probably the existence of the Gulf Stream to the west and north has a
modifying influence upon them, and their action becomes less intense in
that latitude, but they are very similar. I copy a record of the weather,
for a month, which may be found on pages 252, 253, and 254, and a portion
of his remarks:
"The month of December, 1839, presents a continual succession of
revolving winds passing over the Bermudas, with scarcely an
irregularity, as regards the fall and rise of the barometer
accompanying the veering of the wind. One, however, occurred on the
10th and 11th. The S. W. wind abated, and changed to W. N. W., with
the barometer still falling. But in the column of remarks it is noted
that there was lightning seen in the N. and N. W., from 7 P.M.,
during the night. This irregularity may, therefore, have been
occasioned by a gale passing over the banks of Newfoundland,
influencing the direction of the wind at Bermuda.
"REVOLVING WINDS.
+-----------------------------------------------------------------+
| Date. | Hour. |Direction of| Wind's | Weather. | Bar.|Ther.|
| | | Wind. | Force. | | | |
|--------|---------|------------|--------|-----------|------|-----|
| 1839. | | | | | | |
|Nov. 30 |Midnight.| S. S. E. | 1 |b. c. | 30.06| 65 |
|Dec. 1 | Noon. | S. S. W. | 3 |b. c. | 30.07| 71 |
| 2 | " | S. W. | 5 |g. m. q. | 29.86| 70 |
| 3 | " | S. S. W. | 3 |g. c. | 29.76| " |
| 4 | " | S. W. | 6 |g. m. r. | 29.62| 68 |
| 5 | " | W. N. W. | 5 |p. q. | 29.56| " |
| 6 | " | N. W. | 6 |p. q. |*29.55| " |
| 7 | " | N. N. W. | 5 |b. c. | 29.78| 70 |
| " |Midnight.| N. N. W. | 3 |b. c. | 29.89| 68 |
| 8 | Noon. | W. N. W. | 2 |b. c. | 29.82| 71 |
| 9 | " | S. S. W. | 5 |p. q. | 29.84| 70 |
| 10 | " | S. W. | 2 |b. c. | 29.96| " |
| 11 | " | W. N. W. | 6 |b. c. m. |*29.88| 68 |
| 12 | " | S. S. W. | " |b. v. | 29.99| 69 |
| 13 | " | N. N. by W.| " |b. v. | 30.01| 66 |
| 14 | " | N. N. W. | 5 |b. c. v. | 30.06| 64 |
| " |Midnight.| N. W. | 2 |b. c. p. | 30.05| 63 |
| 15 | Noon. | S. W. by S.| 6 |g. m. r. | 29.72| 65 |
| " | P.M. 2 | S. S. W. | 7 |m. q. r. | 29.92| 64 |
| " | " 4 | S. S. W. | " |g. m. q. r.| 29.55| " |
| " | " 6 | W. S. W. | " |q. w. |*29.53| " |
| " | " 8 | N. W. | 6 |b. c. q. | 29.54| " |
| " | " 10 | N. N. W. | " |b. c. | 29.55| " |
| 16 | Noon. | N. W. | 7 |b. c. m. | 29.53| 62 |
| 17 | " | N. W. by N.| " |p. q. | 29.67| 60 |
| 18 | " | N. W. | 6 |c. q. | 29.86| " |
| 19 | " | N. W. by N.| 7 |m. q. r. |*29.73| 59 |
| 20 | " | N. N. W. | " |p. q. c. | 29.89| 58 |
| 21 | " | N. W. by N.| 6 |c. q. | 29.96| 56 |
| " |Midnight.| S. W. | 1 |b. c. | 29.95| 55 |
| 22 | Dawn. | ---- | 0 | | | |
| " | Noon. | S. S. W. | 5 |g. m. | 29.83| 56 |
| " | P.M. 4 | S. | 7 |g. m. | 29.79| " |
| " | " 6 | S. S. E. | " |g. m. r. | 29.61| " |
| " | " 8 | S. S. E. | " |w. r. | 29.52| " |
| " | " 10 | S. E. | " |m. w. r. | 29.48| " |
| 23 | Noon. | S. W. | 6 |b. c. m. |*29.44| 57 |
| 24 | " | W. N. W. | " |b. m. | 29.71| 59 |
| 25 | " | W. N. W. | 5 |b. c. | 29.88| 56 |
| 26 | " | N. | 3 |c. | 30.09| 62 |
| 27 | " | S. E. | 5 |c. q. r. | 30.07| 61 |
| 28 | " | S. W. | 6 |c. q. | 29.88| 66 |
| " |Midnight.| S. S. W. | " |b. c. | 29.76| 65 |
| 29 | Noon. | S. W. | 7 |c. b. |*29.48| 64 |
| 30 | " | W. N. W. | 6 |b. c. q. | 29.83| 55 |
| 31 | " | N. W. | 5 |b. c. | 30.12| 58 |
+-----------------------------------------------------------------+
"_Remark printed in the Register._
"The changes of the wind during the December gales have been nearly
the same in all: _i. e._, commencing with a southerly wind at first,
the wind has veered by the west, toward the north-west, sometimes
ending as far round as N. N. W."
These extracts show the passage of several successive belts, each with the
phenomena in regular order.
The first commences with blue sky and detached clouds, barometer up,
thermometer down to 65 deg., and nearly calm, on the 30th of November.
Dec. 1 (at noon). Wind freshens from S. S. W.; thermometer rises;
barometer still up.
Dec. 2. Barometer has fallen; thermometer up; wind increasing from S. W.,
with gloomy, squally appearance.
Dec. 3. Wind S. S. W.; barometer slowly falling; thermometer slightly.
Dec. 4. Wind fresh; S. W.; condensation and rain has reached them, and it
carries barometer and thermometer down.
Dec. 5. Wind shifting by the west, and squally.
Dec. 6. Winds gets N. W.; blows fresh; barometer at its minimum, probably
at the time of the change of wind, although the register does not show the
precise time.
Dec. 7. Wind N. N. W.; blue sky and detached clouds (N. W. scud), cleared
off; barometer elevated by the N. W. wind, from 29.55 to 29.78. Midnight:
blue sky; detached clouds (N. W. scud probably); barometer up to 29.89;
thermometer fallen, from the cooler character of the northerly wind.
Dec. 8. Wind having lulled as a northerly wind has got round to S. W.
again; thermometer up; barometer falling, and another belt approaching,
and so on.
The first and last part of December show each two regular occurrences of
substantially the same phenomena. The middle is somewhat more irregular.
There were five distinctly-marked periods, and one squally, long-continued
period, with a slight tendency to condensation, and a slight fall of
barometer and rain on the 19th (N. W. squall probably), but not sufficient
to reverse the wind to the south. In Colonel Reid's opinion there were
five revolving gales which passed over Bermuda during the month. In my
opinion, there were five perfect polar waves of condensation, and one
imperfect one, with as many successive southerly winds preceding the
condensation, with or without rain in the center, followed by as many cold
N. W. or N. N. W. winds, with squalls, in the rear, about five days apart.
(See the * in the barometric column.)
_We are at issue._ Let the question be determined by _actual observation_,
and not by _speculation_. It is of fundamental and exceeding importance to
the science.
Now, let us take a month in summer, from the observations of Mr. Bassnett,
at Ottawa. Here the climate differs somewhat from that east of the
Alleghanies; the magnetic intensity is greater, and the action more
violent and irregular. That part of the country, it should be remembered,
has a greater fall of rain in summer, for reasons we have stated, and
those periodic revolutions are more frequent.
"A brief abstract from a journal of the weather for one sidereal
period of the moon, in 1853.
"_June_ 21st. Fine clear morning (S. fresh): noon very warm 88 deg.; 4
P.M., plumous _cirri in south_; ends clear.
"22d. Hazy morning (S. very fresh) arch of cirrus in west; 2 P.M.,
black in W. N. W.; 3 P.M., overcast and rainy; 4 P.M., a heavy gust
from south; 4.30 P.M., blowing furiously (S. by W.); 5 P.M.,
tremendous squall, uprooting trees and scattering chimneys; 6 P.M.,
more moderate (W.).
"23d. Clearing up (N. W.); 8 A.M., quite clear; 11 A.M., bands of
mottled cirri pointing N. E. and S. W., ends cold (W. N. W.); the
cirri seem to rotate from left to right, or with the sun.
"24th. Fine clear, cool day, begins and ends (N. W.).
"25th. Clear morning (N. W. light); 2 P.M. (E.), calm; tufts of
tangled cirri in north, intermixed with radiating streaks, all
passing eastward; ends clear.
"26th. Hazy morning (S. E.), cloudy; noon, a heavy, windy-looking
bank in north (S. fresh), with dense cirrus fringe above, on its
upper edge; clear in S.
"27th. Clear, warm (W.); bank in north; noon bank covered all the
northern sky, and fresh breeze; 10 P.M., a few flashes to the
northward.
"28th. Uniform dense cirro-stratus (S. fresh); noon showers all
round; 2 P.M., a heavy squall of wind, with thunder and rain (S. W.
to N. W.); 8 P.M., a line of heavy cumuli in south; 8.30 P.M., a very
bright and high cumulus in S. W., protruding through a layer of dark
stratus; 8.50 P.M., the cloud bearing E. by S., with three rays of
electric light.
"29th. A stationary stratus over all (S. W. light); clear at night,
but distant lightning in S.
"30th. Stratus clouds (N. E. almost calm); 8 A.M., raining gently; 3
P.M., stratus passing off to S.; 8 P.M., clear, pleasant.
"_July_ 1st. Fine and clear; 8 A.M., cirrus in sheets, curls, wisps,
and gauzy wreaths, with patches beneath of darker shade, all nearly
motionless; close and warm (N. E.); a long, low bank of haze in S.,
with one large cumulus in S. W., but very distant.
"2d. At 5 A.M., overcast generally, with hazy clouds and fog of
prismatic shades, chiefly greenish-yellow; 7 A.M. (S. S. E.
freshening), thick in W.; 8 A.M. (S. fresh), much cirrus, thick and
gloomy; 9 A.M., a clap of thunder, and clouds hurrying to N.; a
reddish haze all around; at noon the margin of a line of
yellowish-red cumuli just visible above a gloomy-looking bank of haze
in N. N. W. (S. very fresh); warm, 86 deg.; more cumuli in N. W.; the
whole line of cumuli N. are separated from the clouds south by a
clearer space. These clouds are borne rapidly past the zenith, but
never get into the clear space--they seem to melt or to be turned off
N. E. The cumuli in N. and N. W., slowly spreading E. and S.; 3 P.M.,
the bank hidden by small cumuli; 4 P.M., very thick in north,
magnificent cumuli visible sometimes through the breaks, and beyond
them a dark, watery back-ground (S. strong); 4.30 P.M., wind round to
N. W. in a severe squall; 5 P.M., heavy rain, with thunder, etc.--all
this time there is a bright sky in the south visible through the rain
15 deg. high; 7 P.M., clearing (S. W. mod.).
"3d. Very fine and clear (N. W.); noon, a line of large cumuli in N.,
and dark lines of stratus below, the cumuli moving eastward; 6 P.M.,
their altitude 2 deg. 40'. Velocity, 1 deg. per minute; 9 P.M., much
lightning in the bank north.
"4th. 6 A.M., a line of small cumulo-stratus, extending east and
west, with a clear horizon north and south 10 deg. high. This band seems
to have been thrown off by the central yesterday, as it moves slowly
south, preserving its parallelism, although the clouds composing it
move eastward. Fine and cool all day (N. W. mod.)--lightning in N.
"5th. Cloudy (N. almost calm), thick in E., clear in W.; same all
day.
"6th. Fine and clear (E. light); small cumuli at noon; clear night.
"7th. Warm (S. E. light); cirrus bank N. W.; noon (S.) thickening in
N.; 6 P.M., hazy but fine; 8 P.M., lightning in N.; 10 P.M., the
lightning shows a heavy line of cumuli along the northern horizon;
calm and very dark, and incessant lightning in N.
"8th. Last night after midnight commencing raining, slowly and
steadily, but leaving a line of lighter sky south; much lightning all
night, but little thunder.
"8th. 6 A.M., very low scud (500 feet high) driving south, still calm
below (N. light); 10 A.M., clearing a little; a bank north, with
cirrus spreading south; same all day; 9 P.M., wind freshening (N.
stormy); heavy cumuli visible in S.; 10.30 P.M., quite clear, but a
dense watery haze obscuring the stars; 12 P.M., again overcast; much
lightning in S. and N. W.
"9th. Last night (2 A.M. of 9th) squall from N. W. very black; 4
A.M., still raining and blowing hard, the sky a perfect blaze, but
very few flashes reach the ground; 7 A.M., raining hard; 8 A.M. (N.
W. strong); a constant roll of thunder; noon (N. E.); 2 P.M. (N.); 4
P.M., clearing; 8 P.M., a line of heavy cumuli in S., but clear in N.
W., N., and N. E.
"10th. 3 A.M., Overcast, and much lightning in south (N. mod.); 7
A.M., clear except in south; 6 P.M. (E.); 10 P.M., lightning south;
11 P.M., auroral rays long, but faint, converging to a point between
Epsilon Virginis and Denebola, in west; low down in west, thick with
haze; on the north the rays converged to a point still lower;
lightning still visible in south. This is an aurora in the west.
"11th. Fine, clear morning (N. E.); same all day; no lightning
visible to-night, but a bank of clouds low down in south, 2 deg. high,
and streaks of dark stratus below the upper margin.
"12th. Fine and clear (N. E.); noon, a well-defined arch in S. W.,
rising slowly; the bank yellowish, with prismatic shades of
greenish-yellow on its borders. This is the O. A. At 6 P.M., the bank
spreading to the northward. At 9 P.M., thick bank of haze in north,
with bright auroral margin; one heavy pyramid of light passed through
Cassiopeia, traveling _westward_ 1-1/2 deg. per minute. This moves to the
other side of the pole, but not more inclined toward it than is due
to prospective, if the shaft is very long; 11.10 P.M., saw a mass of
light more diffuse due east, reaching to _Markab_, then on the prime
vertical. It appears evident this is seen in profile, as it inclines
downward at an angle of 10 deg. or 12 deg. from the perpendicular. It does
not seem very distant. 12 P.M., the aurora still bright, but the
brightest part is now west of the pole, before it was east.
"13th. 6 A.M., clear, east and north; bank of cirrus in N. W., _i.
e._, from N. N. E. to W. by S.; irregular branches of cirrus clouds,
reaching almost to south-eastern horizon; wind changed (S. E. fresh);
8 A.M., the sky a perfect picture; heavy regular shafts of dense
cirrus radiating all around, and diverging from a thick nucleus in
north-west, the spaces between being of clear, blue sky. The shafts
are rotating from north to south, the nucleus advancing eastward.
"At noon (same day), getting thicker (S. E. very fresh); 6 P.M., moon
on meridian, a prismatic gloom in south, and very thick stratus of
all shades; 9 P.M., very gloomy; wind stronger (S. E.); 10 P.M., very
black in south, and overcast generally.
"14th. Last night, above 12 P.M., commenced raining; 3 A.M., rained
steadily; 7 A.M., same weather; 8.20 A.M., a line of low storm-cloud,
or scud, showing very sharp and white on the dark back-ground all
along the southern sky. This line continues until noon, about 10 deg. at
the highest, showing the northern boundary of the storm to the
southward; 8 P.M., same bank visible, although in rapid motion
eastward; same time clear overhead, with cirrus fringe pointing north
from the bank; much lightning in south (W. fresh); so ends.
"15th. Last night a black squall from N. W. passed south without
rain; at 3 A.M., clear above but, very black in south (calm below all
the time); 9 A.M., the bank in south again throwing off rays of cirri
in a well-defined arch, whose vortex is south; these pass east, but
continue to form and preserve their linear direction to the north; no
lightning in south to-night.
"16th. Clear all day, without a stain, and calm.
"17th. Fine and clear (N. E. light); 6 P.M., calm.
"18th. Fair and cloudy (N. E. light); 6 P.M., calm.
"19th. Fine and clear (N. fresh); I. V. visible in S. W.
"20th. 8 A.M., bank in N. W., with beautiful cirrus radiations; 10
A.M., getting thick, with dense plates of cream-colored cirrus
visible through the breaks; gloomy looking all day (N. E. light)."
The letters in a parenthesis signify the direction of the wind.
During this month there were three distinctly marked periods of belts of
showers, preceded by "fresh" or "strong" south wind, and followed by the
N. W. There was a period when a belt of less intense stratus, without much
wind, occurred (28th, 29th, and 30th of June). This was followed by a
distinct belt of showers and _fresh_ S. wind, on the 2d of July, and by
the N. W. wind and clear weather, on the 3d.
During the rest of July it was more irregular, with the exception of the
7th, 8th, and 9th, when another belt and revolution occurred.
Now, these periods, when distinctly marked, exhibit the same succession of
phenomena--viz., elevation of temperature, fresh southerly wind, belt of
condensation, cumulus or stratus with cirrus running east, but extending
south, followed by N. W. wind, and clear, cold air. Can any one believe
they were successive rotary gales?
I wish, in this connection, to make a suggestion to Lieutenant Maury and
others. The descriptions of M. Bassnett, although not perfect, are very
intelligible. He describes things as they were, and as they should be
described. He distinguishes the clouds, and the scud, and other
appearances.
But Colonel Reid's descriptions are unmeaning and unintelligible. G.
M.--Gloomy, misty! Gloomy from what? fog, or stratus, or a stratum of
scud, or what? We can not know. Again, C. The table tells us this stands
for detached clouds. But of what kind? Cumulus, broken stratus, patches of
cirro-cumulus or cirro-stratus, or scud? All these, and indeed every kind
of cloud or fog formation, except low fog, may exist in detached portions.
These abbreviations will not answer; they do not describe the weather. The
clouds must be studied and described. There is no difficulty in doing it.
Sailors will learn them very soon after their teachers have; and those who
teach them should see to it that the logs contain terms of description
which convey the meaning which may, and ought to be, conveyed. The use of
these indefinite terms can not be continued without culpability.
Again, the observations of seamen off our coast are in accordance with the
progress of this class of storms on land, and prove that they continue S.
E. over the Atlantic, abating in action as they approach the tropics.
There is abundant evidence of this in the work of Colonel Reid, and the
charts of Lieutenant Maury, but I can not devote further space to them.
The third class form in the counter-trade, over some portion of the
country, from excessive volume or action of the counter-trade, or local
magnetic activity, without coming from the tropics or being connected with
a regular polar wave of magnetic disturbance.
The following diagram exhibits their form, progress, and accompanying
induced winds.
[Illustration: Fig. 22.]
The gentle rains of spring, particularly April, and the moderate and
frequent snow-storms of winter, are often of this character; and so are
the heavy rains, which commence at the morning barometric minimum, rain
heavily through the forenoon, and light up near mid-day in the south,
followed by gentle, warm, S. W. winds. This class are more frequent in
some years than others--probably the early years of the decade, while
polar storms are, during the later ones. It is this class which have
_violent_ easterly winds _in front_, and on the _south side_, with two or
more currents, and which Mr. Redfield has also supposed to be cyclones.
The fourth class are isolated showers, occurring over particular
localities, or belts of drought and showers alternating; sometimes a
general disposition to cloudy and showery weather for a longer or shorter
interval over the whole country; at others, limited to particular
localities in the course of the trade. Such a period occurred during the
wheat harvest of 1855. This class I attribute to a general increased
magnetic action, but it may be induced by an increased volume, or greater
south polar magnetic intensity of the counter-trade, exciting and
concentrating the regular currents of the field, and increasing their
activity and energy. These also often work off south gradually, and are
followed by a cold N. W. air for a day or two; showing a tendency, in the
excited magnetism, to pass as a wave toward the tropics.
The following diagram will give some idea of this class:
[Illustration: Fig. 23.]
There are sometimes very obvious local tendencies to precipitation over
portions adjoining an area affected with drought, as there are other
magnetic irregularities over particular areas.
All these classes of storms are variant in intensity. Sometimes the
general or local cloud-formation is weak, and does not produce
precipitation at all; so of that which extends southerly. Probably the
tropical storm are always sufficiently dense and active to precipitate.
Their action is often violent over particular localities, and hence the
more frequent occurrence of the tornado over the more intense area of
Ohio, and other portions of the west. All violent local storms are
doubtless owing to local magneto-electric activity.