Chapter X (2)

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.

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:

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.

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:

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.