ARRHENIUS, WORLDS IN THE MAKING

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thelivyjr
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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Wed Nov 27, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM

WE have so far dwelt on the effects which the particles expelled from the sun and the stars exert on distant celestial bodies.

It may be asked whether this dust does not act upon our own earth.

We have already recognized the peculiar luminescence which on clear nights is diffused over the sky as a consequence of electrical discharges of this straying dust.

This leads to the question whether the magnificent polar lights, which according to modern views are also caused by electric discharges in the higher strata of the atmosphere, are not produced by dust which the sun sends to us.

It will, indeed, be seen that we can in this way explain quite a number of the peculiarities of these mysterious phenomena which have always excited man's imagination.

We know that meteorites and shooting-stars are rendered incandescent by the resistance which they encounter in the air at an average height of 120 km. (75 miles), sometimes of 150 and 200 km.

In isolated cases meteorites are supposed to have become visible even at still greater altitudes.

It would result that there must be appreciable quantities of air still at relatively high elevation, and that the atmosphere cannot be imperceptible at an altitude of less than 100 km., as was formerly assumed.

Bodies smaller than the meteorites as well as the solar dust we have spoken of which, owing to their minuteness and to the strong cooling by heat radiation and conduction that they undergo in passing through the atmosphere, could never attain incandescence would be stopped at greater heights.

We will assume that they are arrested at a mean height of about 400 km. (250 miles).

The masses of dust which are expelled by the sun are partly uncharged, partly charged with positive or negative electricity.

Only the latter can be connected with the polar lights; the former would remain dark and slowly sink through our atmosphere to the surface of the earth.

They form the so-called cosmical dust, of whose great importance Nordenskiold was so firmly convinced.

He estimated that the yearly increase in the weight of the earth by the addition of the meteorites was at least ten million tons, or five hundred times more than we stated above (page 108).

Like Lockyer and, in more recent days, Chamberlin, he believed that the planets were largely built up of meteorites.

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thelivyjr
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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Sat Nov 30, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued ...

The dust reaching the earth from the sun would not, were it not electrically charged, amount to more than 200 tons in a year.

Although this figure may be far too low, yet the supply of matter by these means is certainly very small in comparison with the 20,000 tons which the earth receives in the shape of meteorites and shooting-stars.

But owing to its extremely minute distribution, the effect of this dust is very important, and it may constitute a much greater portion of the finely distributed cosmical dust in the highest strata of the atmosphere than the dust introduced by falling meteorites and shooting-stars.

That these particles exert a noticeable influence upon terrestrial conditions, in spite of their relatively insignificant mass, is due to two causes.

They are extremely minute and therefore remain suspended in our atmosphere for long periods (for more than a year in the case of the Krakatoa dust), and they are electrically charged.

In order to understand their action upon the earth, we will examine how the terrestrial conditions depend upon the position of the earth with regard to the various active portions of the sun, and upon the change of the sun itself in regard to its emission of dust particles.

For this examination we have to avail ourselves of extensive statistical data; for only a long series of observations can give us a clear conception of the action of solar dust.

These particles withdraw from the sun gases which they were able to condense on their surface, and which had originally been in the chromosphere and in the corona of the sun.

The most important among these gases is hydrogen; next to it come helium and the other noble gases which Ramsay has discovered in the atmosphere, in which they occur in very small quantities.

As regards hydrogen, Liveing and (after him) Mitchell have maintained that it is not produced in the terrestrial atmosphere.

Occasionally it is certainly found in volcanic gases.

Thus hydrogen escapes, for instance, from the crater of Kilauea, on Hawaii, but it is burned at once in the atmosphere.

If hydrogen were present in the atmosphere, it would gradually combine with the oxygen to water vapor; and we have to assume, therefore, that the hydrogen must be introduced into our atmosphere from another source namely, from the sun.

Mitchell finds in this view a strong support for the opinion that solar dust is always trickling down through our atmosphere.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Sun Dec 01, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

The quantity of solar dust which reaches our atmosphere will naturally vary in proportion with the eruptive activity of the sun.

The quantity of dust in the higher strata influences the color of the light of the sun.

After the eruption of the volcano Rakata on Krakatoa, in 1883, and again, though to a lesser degree, after the eruption of Mont Pelee on Martinique, red sunsets and sunrises were observed all over the globe.

At the same time, another phenomenon was noticed which could be estimated quantitatively.

The light of the sky is polarized with the exception of the light coming from a few particular spots.

Of these spots, one called Arago's Point is situated a little above the antipode of the sun, and another, Babinet's Point, is situated above the sun.

If we determine the elevation of these points above the horizon at sunset, we find in accordance with the theoretical deduction that this elevation is greater when the higher strata of the atmosphere are charged with dust (as after the eruption of Rakata) than under normal conditions.

Busch, a German scientist, analyzed the mean elevation of these points (stated in degrees of arc) at sunset.

There is a distinct parallelism in these series of figures.

Almost simultaneously with the sun-spot maximum the height of the two so-called neutral points above the horizon attains its maximum at sunset, and the same applies to the minimum.

That the phenomena in the atmosphere take place a little later than the phenomena on the sun which caused them is perhaps only natural.

When the air is rich in dust, or when it is strongly ionized by kathode rays, conditions are favorable for the formation of clouds.

This can be observed, for instance, with auroral lights.

They regularly give rise to a characteristic cloud formation, so much so that Adam Paulsen was able to recognize polar lights by the aid of these clouds in full daylight.

Klein has compiled a table on the connection between the frequency of the higher clouds, the so-called cirrus clouds, at Cologne, and the number of sun-spots during the period 1850-1900.

He demonstrates that during this half-century, which comprises more than four sun-spot periods, the sun-spot maxima fell in the years in which the greatest number of cirrus clouds had been observed.


The minima of the two phenomena are likewise in agreement.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Mon Dec 02, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

A similarly intensified formation of clouds seems also to occur on Jupiter when sun-spots are frequent.

Vogel states that Jupiter at such times shines with a whiter light, while at sun-spot minima it appears of a deeper red.

The deeper we are able to peep into the atmosphere of Jupiter, the more reddish it appears.

During periods of strong solar activity the higher portions of Jupiter's atmosphere therefore appear to be crowded with clouds.

The discharge of the charged solar dust in our atmosphere calls forth the polar lights.

The polar lights occur, as the name indicates, most frequently in the districts about the poles of the earth.

They are, however, not actually more frequent the nearer we come to the poles; but they attain a maximum of frequency in circles which enclose the magnetic and the geographical poles.

The northern maximum belt passes, via Cape Tscheljuskin, north of Novaja Semija, along the northwestern coast of Norway, a few degrees to the south of Iceland and Greenland, right across Hudson Bay and over the northwestern extension of Alaska.

When we go to the south of this belt, the auroras, or boreal lights, diminish markedly.

They are four times less frequent in Edinburgh, and fifteen times less frequent in London or New York, than in the Orkney Islands or Labrador.

Paulsen divides the auroras into two classes, which behave quite differently in several respects.

The great difficulties which the solution of the problems of polar lights has so far offered seem to a large extent to be due to the fact that all polar lights were treated as being of the same kind.

The polar lights of the first class do not display any streamers.

They cover a large portion of the sky in a horizontal direction.

They are very quiet, and their light is strikingly constant.

As a rule, they drift slowly towards the zenith, and they do not give rise to any magnetic disturbances.

These polar lights generally have the shape of an arch whose apex is situated in the direction of the magnetic meridian (Fig. 38).

Sometimes several arches are grouped one above another.

Nordenskiold observed these arches quite regularly during the polar night when he was wintering near Pitlekaj, in the neighborhood of Bering Sound.

Adam Paulsen has often seen them on Iceland and Greenland, which are situated within the maximum belt spoken of, where northern lights are very common.

Occasionally, auroras are also seen farther from the poles, as circular arches of a milky white, which may be quite high in the heavens.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Thu Dec 05, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

Sometimes we perceive in the arctic regions that large areas of the heavens are covered by a diffused light which might best be compared to a luminous, transparent cloud; the darker portions in it probably appear dark by contrast.

This phenomenon was frequently observed during the Swedish expedition of 1882-1883, near Cape Thordsen.

Masses of light at so low a level that the rocks behind them are obscured have frequently been observed to float in the air, especially in the arctic districts.

Thus Lemstrom saw an aurora on the island of Spitzbergen in front of a wall of rock only 300 m. (1000 ft.) in height.

In northern Finland he observed the auroral line in the light of the air in front of a black cloth only a few metres distant.

Adam Paulsen counts these phenomena also as polar lights of the first class, and he regards them as phosphorescent clouds which have been carried down by convection currents to an unusually low level of our atmosphere.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Fri Dec 06, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

Polar lights of the second class are distinguished by the characteristic auroral rays or streamers.

Sometimes these streamers are quite separated from one another (see Fig. 39); as a rule they melt into one another, especially below, so as to form draperies which are so easily moved and unsteady that they appear to flutter in the wind (Fig. 41.)

The streamers run very approximately in the direction of the inclination (magnetic dip) needle, and when they are fully developed around the celestial dome their point of convergence is distinctly discernible in the so-called corona (Fig. 40).

When the light is at its greatest intensity the aurora is traversed by numerous waves of light.

The draperies are very thin.

Paulsen watched them sometimes drifting over his head in Greenland.

The draperies then appeared foreshortened, in the shape of striae or ribbons of light in convolutions.

These polar lights influence the magnetic needle.

When they pass the zenith their influence changes sign, so that the deviation of the magnetic needle changes from east to west when the ribbon is moving from north to south.


Paulsen therefore concluded that negative electricity (kathode rays) was moving downward in these rays.

These polar lights correspond to violent displacements of negative electricity, while polar lights of the first class appear to consist of a phosphorescent matter which is not in strong agitation.

The streamers may penetrate down into rather low atmospheric strata, at least in districts which are near the maximum belt of the northern lights.

Thus Parry observed at Port Bowen an auroral streamer in front of a cliff only 214 m. (700 ft.) in height.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Sat Dec 07, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

Polar lights of the first order may pass into those of the second order, and vice versa.

We frequently see rays suddenly flash out from the arch of the aurora, mostly downward, but, when the display is very intense, also upward.

On the other hand, the violent agitation of a "drapery light" may cease, and may give way to a diffused, steady glow in the sky.

The polar light of the first class is chiefly observed in the arctic regions.

To it corresponds, in districts farther removed from the pole, the diffused light which appears to be spread uniformly over the heavens and which gives the auroral line.

The usually observed polar lights (speaking not only of those seen on arctic expeditions) belong to the second class, which comprises also all those included in the subjoined statistics, with the exception of the auroral displays reported from Iceland and Greenland.

While the streamer lights distinctly conform to the 11.1 years' period, and become more frequent at times of sun-spot maxima, this is not the case, according to Tromholt, with the auroras of Iceland and Greenland.

Their frequency, on the contrary, seems to be rather independent of the sun-spot frequency.

Not rarely auroral maxima corresponding to sun-spot maxima are subdivided into two by a secondary minimum.

This phenomenon is most evident in the polar regions, but it can also be traced in the statistics from Scandinavia and from other countries.

Better to understand the nature of auroras, we will consider the sun's corona during the time of a minimum year, taking as an example the year 1900 (compare Fig. 30).

The rays of the corona in the neighborhood of the poles of the sun are laterally deflected by the action of the magnetic lines of force of the sun.

The small, negatively charged particles have evidently only a low velocity, so that they move quite close to the lines of force in the neighborhood of the solar poles and are concentrated near the equator.

There the lines of force are less crowded that is to say, the magnetic forces are weaker and the solar dust can therefore be ejected by the radiation pressure and will accumulate to a large disk expanding in the equatorial plane.

To us this disk appears like two large streams of rays which project in the direction of the solar equator.

Part of this solar dust will come near the earth and be deflected by the magnetic lines of force of the earth; it will hence be divided into two streams which are directed towards the two terrestrial magnetic poles.

These poles are situated below the earth's crust, and therefore not all the rays will be concentrated towards the apparent position of the magnetic poles upon the surface of the earth.

It is to be expected that the negatively charged particles coming from the sun will chiefly drift towards that district which is situated somewhat to the south of the magnetic north pole, when it is noon at this pole.

When it is midnight at the magnetic pole, most of the negatively charged particles will be caught by the lines of force before they pass the geographical north pole, and the maximum belt of the auroras will for this reason surround the magnetic and the geographical poles, as has already been pointed out (compare page 122).

The negatively charged solar dust will thus be concentrated in two rings above the maximum belts of the polar lights.

Where the dust collides with molecules of the air, it will produce a phosphorescent glow, as if these molecules were hit by the electrically charged particles of radium.

This phosphorescent glow rises in the shape of a luminous arch to a height of about 400 km. (250 miles) according to Paulsen and the apex of this arch will in every part seem to lie in the direction where the maximum belt is nearest to the station of the observer.

That will fairly coincide with the direction of the magnetic needle.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Mon Dec 09, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

The solar corona of a sun-spot maximum year is of a very different appearance (Fig. 31).

The streamers radiate straight from the sun in almost all directions; and if there be some privileged directions, it will be those above the sun-spot belts.

The velocity of the solar dust is evidently so great that the streamers are no longer visibly deflected by the magnetic lines of force of the sun.

Nor is this charged dust influenced to any noticeable degree by the magnetic lines of force of the earth.

It will in the main fall straight down in that part of the atmosphere in which the radiation is most intense.

As these "hard" rays of the sun seem to issue from the faculse of the sun which are most frequent in maximum sun-spot years, some polar lights will also be seen in districts which are far removed from the maximum belt of the auroras, especially when the number of sun-spots is large.

The opposite relation holds for the "soft" streams of solar dust which fall near the maximum belt of the polar lights.

These streams occur most frequently with low sun-spot frequency, as we know from observations of the solar corona.

Possibly they are carried along by the stream of harder rays in maximum years.

The polar lights corresponding to these rays therefore attain their maximum with few sun-spots.

Hard and soft dust streams occur, of course, simultaneously; but the former predominate in maximum sun-spot years, the latter in minimum years.

NOTE: The designations "hard" and "soft" streams of solar dust correspond to the terms used with regard to kathode rays.

The soft rays have a smaller velocity, and are therefore more strongly deflected by external forces, as, for instance, magnetic forces.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Tue Dec 10, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

That the periodicity of the polar lights in regions without, the maximum belt follows very closely the periodicity of the sun-spots was shown by Fritz as early as 1863.

The length of the period varies between 7 and 16 years, the average being 11.1 years.

The years of maxima and minima for sun-spots and for northern auroras are the following:

MAXIMUM YEARS

Sun-spots: 1728 '39 '50 '62 '70 '78 '88 1804 '16 '30 1837 '48 '60 '71 '83 '93 1905

Northern lights: 1730 '41 '49 '61 '73 '78 '88 1805 '19 '30 1840 '50 '62 '71 '82 '93 1905

MINIMUM YEARS

Sun-spots: 1734 '45 '55 '67 '76 '85 '98 1811 '23 '34 1844 '56 '67 '78 '89 1900

Northern lights: 1735 '44 '55 '66 '75 '83 '99 1811 '22 '34 1844 '56 '66 '78 '89 1900

There are, in addition, as De Mairan proved in his classical memoir of the year 1746, longer periods common to both the number of sun-spots and the number of auroras.

According to Hansky, the length of this period is 72 years; according to Schuster, 33 years.

Very pronounced maxima occurred at the beginning and the end of the eighteenth century, the last in the year 1788; afterwards auroras became very rare in the years 1800-1830, just as in the middle of the eighteenth century.

In 1850, and particularly in 1871, there were strong maxima; they have been absent since then.

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Re: ARRHENIUS, WORLDS IN THE MAKING

Post by thelivyjr » Wed Dec 11, 2019 1:40 p

V - THE SOLAR DUST IN THE ATMOSPHERE POLAR LIGHTS AND THE VARIATIONS OF TERRESTRIAL MAGNETISM, continued …

The estimates of the heights of the polar lights vary very considerably.

The height seems to be the greater, on the whole, the nearer the point of observation is to the equator, which would well agree with the slight deflection of the kathode rays towards the surface of the earth in regions which are farther removed from the pole.

Gyllenskiold found on Spitzbergen a mean height of 55 km.; Bravais, in northern Norway, 100 to 200 km; De Mairan, in central Europe, 900 km.; Galle, again, 300 km.

In Greenland, Paulsen observed northern lights at very low levels.

In Iceland he fixed the apex of the northern arch which may be considered as a point where the charged particles from the sun are discharged into the air at about 400 km.

Not much reliance can be placed upon the earlier determinations; but the heights given conform approximately to the order of magnitude which we may deduce from the height at which the solar dust will be stopped by the terrestrial atmosphere.

The polar lights possess, further, a pronounced yearly periodicity which is easily explicable by the aid of the solar dust theory.

We have seen that sun-spots are rarely observed near the solar equator, and the same applies to solar faculrc.

They rapidly increase in frequency with higher latitudes of the sun, and their maximum occurs at latitudes of about fifteen degrees.

The equatorial plane of the sun is inclined by about seven degrees towards the plane of the earth's orbit.

The earth is in the equatorial plane of the sun on December 6th and June 4th, and most distant from it three months later.

We may, therefore, expect that the smallest number of solar-dust particles will fall on the earth when the earth is in the equator of the sun that is, in December and June and the greatest number in March and September.

These relations are somewhat disturbed by the twilight, which interferes with the observation of auroras in the bright summer nights of the arctic region, while the dark nights of the winter favor the observation of these phenomena.

TO BE CONTINUED ...

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