light, and its movements are controlled by the earth's magnetic force, in a manner analogous to the influence of an artificial magnet upon a current of electricity circulating around it."

DARKNESS AND COLD OF SPACE.

To see the atmosphere of our planet, and the planet within the enveloping sea of air, an ocean of mingled gases at the bottom of which we have our life, it may be noted first that all space surrounding us, even that through which we look to the sun by day, and in our hottest season, is an absolute of darkness and of cold. If we could be placed in open space some distance beyond our atmosphere we would see the sun, through total darkness, as a bright orb, but not apparently giving any light to space, and the earth as an orb also, simply bright with reflected light, but not light-giving. Our sunlight by day and our moonlight by night are phenomena possible only within the limits of our atmosphere, and not possible anywhere in the depths of space. The rays radiated from the sun through space do not constitute or carry light in any way whatever, until they encounter conditions such as those of the atmosphere surrounding the globe, and produce among those conditions the effect which we know as light.

The agency acting from the sun through space has what are understood as vibratory effects of very wide variety as to the comparative rapidity of the vibrations produced, and the whole breadth of these effects is called the solar spectrum. As we pass from right to left across the page on which we represent this spectrum, a considerable length of it has vibrations too small to give the effect of light to our eyes; then we begin at violet and pass through the colors to red; and beyond that, for an extended section of rays of very marked power, we have an invisible spectrum of perhaps ten times the length of that within which we get the light effects from violet to red. This plainly reveals the fact that even within the conditions of our atmosphere light is the effect of a very limited section only of the broad spectrum of rays which come through space from the sun; and research has demonstrated that even this narrowly limited pencil of rays gives no effect of light as it passes through space, and only becomes light-producing when it enters

our atmosphere and as it comes to the surface of the earth.

Prof. A. E. Dolbear has lately said: "For a long time it was believed there were three different kinds of ether waves, known as heat, light, and actinic rays. The latter were supposed to be the ones that produced the chemical action on photographic plates, while light consisted of rays of a different kind, capable of affecting the eye. It was discovered, however, that the same rays that can produce vision can also heat a body, and also do photographic work; and what any ray can do depends upon the kind of matter it falls upon, so that all rays have similar characteristic properties. The discovery makes it plain that there is no peculiar kind of ether waves which can be called light, as distinguished from other kinds of ether waves. What is called light is a physiological phenomenon and has no existence apart from eyes. So well assured is this, that the serious proposal is made to banish the word 'light' from physics."

The differences which have been noted, and correctly noted, are those of waves varying in amplitude, those of least amplitude on the extreme right of the solar spectrum, and noted as actinic with reference to their chemical action, and those of the greatest amplitude on the extreme left, and noted as heat waves, because of their marked heating effect. There may be heating effect, and in fact must be, from any of the waves the whole length of the spectrum, and there might be chemical effects at any point of the spectrum, but the fact remains that, while notable chemical effects begin on the extreme right of the spectrum, marked heating effects fall far to the left. Thus, Tyndall found that the quality of the heat radiated by a flame of hydrogen is almost exclusively ultra-red. The general distinction is, therefore, fully warranted, which notes as specially chemical the right-hand part of the spectrum, and as specially that of heat effects the lefthand end of the spectrum. And there is no question whatever that in a particular place of the solar spectrum, and only a short space, occur waves which are of the right amplitude to give the light effect to our eyes.

Tyndall found that of the emission from a dazzling electric-light, one-tenth only consists of luminous rays, and that

nearly two-thirds of the rays from the electric-light which actually reach the retina are obscure. Of the emission from the most brilliant portion of a gas-flame, he found that one-twenty-fifth only consists of luminous rays; and that of the radiation from platinum, heated to whiteness, only one-twenty-fourth consists of luminous rays.

The reason for this, although it has never been noted, is a simple one. The eye is prepared for seeing by the action of the oxygen of respiration, and those waves serve to give the effect of light to the eye which synchronize with those of oxygen. Sachs shows how in plants the evolution of oxygen from the organs containing chlorophyll depends on a certain range of wave-lengths in the spectrum of light. He shows the extremes between which the sunlight effects the separation of the oxygen, and the point between at which the effect is at a maximum.

"The evolution of oxygen," he says, "begins in the blue light, ascends through the green of the spectrum up to the middle of the yellow, and there reaching its highest point, again descends in the orange-colored rays, to cease within the red portion of the spectrum."

And again he says:

"The decomposition or carbon dioxide in the plant evidently depends upon a photochemical effect. Draper found that the effect in the red portion is extremely feeble, rising quickly in the red-orange, and reaching a maximum in the yellow-green, to fall again in the blue to an extremely small quantity. It is the yellow light which is the effective constituent of daylight in the nutrition of the plant; all direct observations show that the maximum evolution of oxygen takes place in yellow light."

This evidence as to the relation of oxygen to the spectrum is in harmony with other proofs going to show that oxygen, by its range of vibrations, determines within what limits "the electrical organ" which Hertz calls the eye, can receive from solar vibrations the effect of light. The eye is tuned by the vibrations of the oxygen of respiration.

The sun sends a range of vibrations, into a particular part of which falls the range of oxygen vibrations, and within this part only do solar vibrations give the effect of light to our eyes. And that

effect for filling space is limited to the near part of space surrounding the earth, the vast range of space at a distance from the earth being without what we know as light.

And what is true of the light effects of the sun's rays is also true of the heat effects; they are entirely unknown in the regions of space between the sun and the earth. An ascent into the air in a balloon to the height of seven miles, at no matter what season of the year nor with what heat at the surface of the earth, shows a beginning of intense cold, the terrors of which must steadily increase as we recede from the lighted and warmed surface of our planet.

The air, in a much .arer and weaker state than close to the earth, may last to a great height-50 or 100 or 500 milesbut the utmost intensity of the sun's rays descends through it without any effect of heat or warmth, and there shuts down forever upon the lower range of our atmosphere an inconceivable terror of cold accompanied beyond, through the immensities of space, with a limitless blackness of eternal night.

AIR LIFE-SUSTAINING ONLY NEAR THE

EARTH

And we may note here, without any special inquiry as yet into the part played by the oxygen of our atmosphere as the universal breath of life to all living things, that the sea of oxygen gas, mingled with a four-fold amount of nitrogen gas, which forms nearly the whole mass of our atmosphere, does not extend in life-sustaining amount and strength more than about seven miles from the surface of the earth.

Even high among the mountains of a country like Switzerland, the mass of oxygen in the air available for our breathing has become so much rarer than at the ordinary level as to necessitate a more vigorous effort of breathing, in order, by greater exertion, to get an adequate amount of oxygen into the system; and, as the balloon rises into space, the difficulty of an adequate oxygen supply increases, until, at six or seven miles from the bottom of the sea of air, there is not enough to make sure of motion in the limbs, energy in the brain, or even a flickering vitality in the body.

The account in the Encyclopædia Brit

annica article, "Aeronautics,"* of a memorable ascent to a height of seven miles, or 39,000 feet, by Messrs. Glaisher and Coxwell, shows in the most striking manner how the failure of the oxygen supply at that height stops all power of movement in the various parts of the body, one after the other, as they fail to get oxygen, and finally suspends all conscious sensibility, and leaves no possibility, in the intense cold of that elevation, but of speedy death.

INCALCULABLE ELECTRICAL EFFECTS, THROUGH THE AIR, OF THE

SUN'S RAYS

But when we have thus brought within the limit of environing facts our view of the atmosphere, as for all purposes of advantage to life on the earth, an envelope of gaseous substances but a few miles in depth (or in height above our heads), it cannot be too distinctly recognized that almost incalculable effects reach us at the bottom of the atmospheric sea from the sun's immensity and activity. Distant as the sun is, and immense as are the spaces of eternal cold and night through which his influences must travel, the overwhelming storms of solar energy playing about mountains 300 miles high, rolling thousands of miles in depth over the surface of the solar orb, and thrusting tongues of lightning a hundred thousand miles into space, easily and instantly transmit to the receptive constituents of our atmosphere a variety and an aggregate of effects, our uninstructed observation of which suggests a very near and close connection between sun and earth and a path of the solar power flooded all the way with heat and light.

The fact is that to the purely electrical emanations which are the cause of both light and heat from the sun, no aids on the path are needed; nothing but the changeless continuity of the ether of universal space, and those effects which are brightness and warmth to us are the response of mundane and atmospheric conditions to the electric thrills from the sun. Light we have come to very fully under

*The account is quoted elsewhere, as evidence in regard to the instant and absolute dependence of life, not upon chemical action in the body, but upon the constant inrush of the oxygen of respiration, with an immediately physical animating and vitalizing effect.

stand as electrically caused. Heat is no less of purely electrical origin. Lord Kelvin, in a Royal Institution lecture on "The Origin of Motive Power," has said:

"In a series of admirable researches on the agency of electricity in transformations of energy, Joule showed that the chemical combinations taking place in a galvanic battery may be directed to produce a large, probably in some forms of battery an unlimited, proportion of their heat; not in the locality of combination, but in a metallic wire at any distance from that locality.* Thus, if we allow zinc to combine with oxygen by the beautiful process which Grove has given in his battery, we find developed in a wire connecting the two poles the heat which would have appeared directly if the zinc had been burned in oxygen gas.'

Faraday estimated that so minute a portion of water as 25 grains-about 25 drops-has its atoms of oxygen and hydrogen locked together by a quantity of electricity, and requiring another equal amount of electricity to shake them apart into gases, the current effects of which would keep any length of platina wire of 1 of an inch diameter red hot for an hour and a half; and Wheatstone estimated that these current effects would appear in one second at a distance of 576,000 miles. The quantity of power connected with the excitement of so small an amount of water, to shake its atoms apart and permit the formation of molecules of the two component gases, Faraday said equalled that of "a most destructive thunder-storm."

In the combination, Faraday tells us,

*Joule's memorial papers were:

On the Production of Heat by Voltaic Electricity"; Roy. Soc. Proc., Dec. 17, 1840:

On the Heat Evolved by Metallic Conductors of Electricity, and in the Cells of a Battery during Electrolysis"; Oct., 1841:

"On the Electrical Origin of the Heat of Combustion"; Mar., 1843:

"On the Heat Evolved during the Electrolysis of Water"; 1843:

"On the Calorific Effects of Magneto-Electricity."

†Chemical expression is made deplorably inaccurate under the entirely false and misleading conception of "attraction." There is no action of the zinc combining with oxygen. The action is that of the oxygen dashing upon and consuming the zinc. The dash of the oxygen throws off electricity; in the battery or in our fires; and the heat caused is from this thrownoff electricity, not from that which operates combination.

of oxygen and hydrogen to form water, electric powers to a most enormous amount are for the time active, but no examination which we can make of the flame which they form during their energetic clashing together shows us any signs of what is going on, save those which are purely incidental, and are incomparably small in relation to the forces concerned.

No

It is in the same unnoticed way that electrical energy, beyond all imaginable limit in amount, may be operative between the sun and the earth, emanating from the vastness and the intensity of the solar fire-ball, and acting through the mass of our atmosphere as unobserved as the lines of force of the magnet. principle lies deeper in nature than that of the likeness of the kingdom of force to the kingdom of spirit, in that it cometh not with observation, does not submit itself to our inspection for anything more than relatively unimportant incidentals, and has to be comprehended by imagination and faith. Tyndall saw this when he said:

"The ultimate problem of physics is to reduce matter, by analysis, to its lowest conditions of divisibility; and force, to its simplest manifestations; and then, by synthesis, to construct from these elements the world as it stands. We are still a long way from the final solution of this problem; and when the solution comes, it will be one more of spiritual insight than of actual observation."

Tyndall was too far from a clear conception of the problem to state it accurately; Faraday saw more clearly when he doubted the good of chasing atoms through the possibilities of divisibility, and conceived that of what are called atoms we need rather to know what moving agency attends them, handles them, and gives them their place, of action or of hold-fast combination; but it was truly and well said that at the bounds of actual observation thought passes on alone to penetrate the realm of final facts.

Of that realm, the gates ajar of profoundest insight not only permit, but command the utmost endeavor of imagination and effort of faith to follow electric agency in the whole making and maintenance of the cosmos of order and power, in sun or star or earth; and nowhere more than in the vast urns of our atmosphere and the vast fountains of the sun, from which are

filled the capacities of all moving and living things.

How the sun rules the kingdoms of nature and of life through the effects which it operates in the realm of atmospheric conditions under which these kingdoms lie, has been very imperfectly comprehended and very inadequately or erroneously explained; but the great fact is rightly making a stronger and stronger impression with every fresh enlargement of knowledge, and no possible hope of better science can be cherished than that of a complete comprehension of the part played by the enveloping atmosphere of our planet for everything that moves and lives upon it.

DIFFERENT RELATION TO THE SUN OF THE TWO HEMISPHERES OF THE EARTH.

An

Owing to the eccentricity of the earth's orbit, it travels around the sun at a varying rate through the different periods of the year, and is at a varying distance from the sun. About ten days after midwinter of the northern hemisphere, the earth is at her nearest to the sun. important difference is thus established between the seasons of the two hemispheres. In the northern we have the sun farthest from us a few days after midsummer, while at the corresponding season in winter the sun is at his nearest. So far, then, as the sun's distance is concerned, the seasons are rendered more moderate for the northern hemisphere by the effects of the earth's eccentricity. Nor is the difference on this account by any means inconsiderable. The earth receives about one-fifteenth more heat in aphelion than in perihelion. And in winter the earth moves more rapidly than in summer, so that the interval from the autumnal to the vernal equinox is shorter than that from the vernal to the autumnal. Thus, for us, the winter cold is less enduring than the summer heat.

In the southern hemisphere all these relations are reversed. The summer heat is rendered more intense by the greater proximity of the sun, and the winter cold is intensified by his increased distance. The summer heat, also, is less enduring than the winter cold. We have in the north a relatively short, but moderate winter, so far as the sun's proximity can moderate winter cold, and a long,

but also moderate summer. In the southern hemisphere they have a short and intensely hot summer, and a long and intense winter. The presence of a great expanse of sea in the southern hemisphere partially tends to moderate the seasonal changes; but we see in the wider extension of the antarctic snows the effect of the long and the cold winter and the short summer.*

HEAT EFFECTS OF THE SUN DEPEND ON CHARACTER OF THE AIR.

The possible effect of an atmosphere in confining beneath it the heat effects which have reached the surface of the earth, may be illustrated by what Tyndall says of a gas the power of which to stop the upward radiation of heat is extremely great. Tyndall's statement is this:

"Were our globe encircled by a shell of olefiant gas two inches in thickness, the shell would offer a scarcely sensible obstacle to the passage of the solar rays earthward, but it would intercept, and in great part return, 33 per cent. of the terrestrial radiation. Under such a canopy, trifling as it may appear, the surface of the earth would be kept at a stifling temperature. The possible influence of an atmospheric envelope on the temperature of a planet is here most forcibly illustrated."

Neither the nitrogen nor the oxygen of the atmosphere would have any such effect. It is to aqueous vapor in the air that all such effect is due. Tyndall says:

"Our atmosphere produces a local heightening of the temperature at the earth's surface. The chief intercepting substance is the aqueous vapor of the atmosphere, the oxygen and nitrogen of which the great mass of the atmosphere is composed being sensibly transparent to the calorific rays. Were the atmosphere cleansed of its vapor the temperature of space would be directly open to us."

AQUEOUS VAPOR IN THE AIR CONTROLS

TEMPERATURE.

This means that without aqueous vapor in the air the heat effects which reach the earth would be so thrown back into

space, except at the moment, as to give no continuous elevation of temperature.

*E. B., Vol. II. 795.

The direct rays of the sun would be hotter in falling, only to be followed by intense cold after their withdrawal. In order to have any continuous elevation of temperature, an atmosphere must supply some means of absorbing heat, and of throwing back the radiation, upward, of heat from the surface of the earth. Aqueous vapor in the air is a most effective means, because of its exceptional power to absord the heat effects, and to radiate them back to the earth.

"Weight for weight," says Tyndall, 'aqueous vapor transcends all others in absorptive power. The power of the water molecule as a radiant and an absorbent is perfectly unprecedented and anomalous. That ten per cent. of the entire terrestrial radiation is absorbed by the aqueous vapor which exists within ten feet of the earth's surface on a day of average humidity, is a moderate estimate. The aqueous vapor exercises a powerful absorption on the invisible calorific rays of the sun, which experiment shows to be about twice the visible."

It was in view of facts such as these that Tyndall, speaking of the effect of our atmosphere on solar and terrestrial heat, said: "It is exceedingly probable that the absorption of the solar rays by the atmosphere is mainly due to the watery vapor contained in the air. The vast difference between the temperature of the sun at midday and in the evening [i. e. early evening, before sundown], is also probably due, in the main, to that comparatively shallow stratum of aqueous vapor which lies close to the earth. At noon the depth of it pierced by the sunbeams is very small; in the evening very great in comparison. The intense heat of the sun's direct rays on high mountains is due to the comparative absence of aqueous vapor at those great elevations. But this vapor, which exer、 cises such a destructive action on the obscure rays, is comparatively transparent to the rays of light. Hence the differential action of the heat coming from the sun to the earth, and that radiated from the earth into space, is vastly augmented by the aqueous vapor of the atmosphere. De Saussure, Fourier, M. Pouillet, and Mr. Hopkins regard this interception of the terrestrial rays as exercising a most important influence on climate. Now if, as experiments indicate, the chief influence be exercised by the aqueous vapor,