Part 4 (1/2)

Let us turn again to chemistry, and see where experiments performed in cosmic laboratories can serve as a guide to the investigator.

A spinning solar tornado, incomparably greater in scale than the devastating whirlwinds that so often cut narrow paths of destruction through town and country in the Middle West, gradually gives rise to a sun-spot. The expansion produced by the centrifugal force at the centre of the storm cools the intensely hot gases of the solar atmosphere to a point where chemical union can occur. t.i.tanium and oxygen, too hot to combine in most regions of the sun, join to form the vapor of t.i.tanium oxide, characterized in the sunspot spectrum by fluted bands, made up of hundreds of regularly s.p.a.ced lines. Similarly magnesium and hydrogen combine as magnesium hydride and calcium and hydrogen form calcium hydride. None of these compounds, stable at the high temperatures of sun-spots, has been much studied in the laboratory. The regions in which they exist, though cooler than the general atmosphere of the sun, are at temperatures of several thousand degrees, attained in our laboratories only with the aid of such devices as powerful electric furnaces.

[Ill.u.s.tration: Fig. 34. Splitting of spectrum lines by a magnetic field (Babc.o.c.k).

The upper and lower strips show lines in the spectrum of chromium, observed without a magnetic field. When subjected to the influence of magnetism, these single lines are split into several components.

Thus the first line on the right is resolved by the field into three components, one of which (plane polarized) appears in the second strip, while the other two, which are polarized in a plane at right angles to that of the middle component, are shown on the third strip. The next line is split by the magnetic field into twelve components, four of which appear in the second strip and eight in the third. The magnetic fields in sun-spots affect these lines in precisely the same way.]

It is interesting to follow our line of reasoning to the stars, which differ widely in temperature at various stages in their life-cycle.[*] A sun-spot is a solar tornado, wherein the intensely hot solar vapors are cooled by expansion, giving rise to the compounds already named. A red star, in Russell's scheme of stellar evolution, is a cooler sun, vast in volume and far more tenuous than atmospheric air when in the initial period of the ”giant” stage, but compressed and denser than water in the ”dwarf” stage, into which our sun has already entered as it gradually approaches the last phases of its existence. Therefore we should find, throughout the entire atmosphere of such stars, some of the same compounds that are produced within the comparatively small limits of a sun-spot. This, of course, on the correct a.s.sumption that sun and stars are made of the same substances. Fowler has already identified the bands of t.i.tanium oxide in such red stars as the giant Betelgeuse, and in others of its cla.s.s. It is safe to predict that an interesting chapter in the chemistry of the future will be based upon the study of such compounds, both in the laboratory and under the progressive temperature conditions afforded by the countless stellar ”giants”

and ”dwarfs” that precede and follow the solar state.

[Footnote *: See Chapter II.]

[Ill.u.s.tration: Fig. 35. Electric furnace in the Pasadena laboratory of the Mount Wilson Observatory.

With which the chemical phenomena observed in sun-spots and red stars are experimentally imitated.]

ASTROPHYSICAL LABORATORIES

It is precisely in this long sequence of physical and chemical changes that the astrophysicist and the astrochemist can find the means of pus.h.i.+ng home their attack. It is true, of course, that the laboratory investigator has a great advantage in his ability to control his experiments, and to vary their progress at will.

But by judicious use of the transcendental temperatures, far out ranging those of his furnaces, and extreme conditions, which he can only partially imitate, afforded by the sun, stars, and nebulae, he may greatly widen the range of his inquiries. The sequence of phenomena seen during the growth of a sun-spot, or the observation of spots of different sizes, and the long series of successive steps that mark the rise and decay of stellar life, resemble the changes that the experimenter brings about as he increases and diminishes the current in the coils of his magnet or raises and lowers the temperature of his electric furnace, examining from time to time the spectrum of the glowing vapors, and noting the changes shown by the varying appearance of their lines.

[Ill.u.s.tration: Fig. 36. t.i.tanium oxide in red stars.

The upper spectrum is that of t.i.tanium in the flame of the electric arc, where its combination with oxygen gives rise to the bands of t.i.tanium oxide (Fowler). The lower strip shows the spectrum of the red star Mira (Omicron Ceti), as drawn by Cortie at Stonyhurst.

The bands of t.i.tanium oxide are clearly present in the star.]

[Ill.u.s.tration: Fig. 37. t.i.tanium oxide in sun-spots.

The upper strip shows a portion of the spectrum of a sun-spot (Ellerman); the lower one the corresponding region of the spectrum of t.i.tanium oxide (King). The fluted bands of the oxide spectrum are easily identified in the spot, where they indicate that t.i.tanium and oxygen, too hot to combine in the solar atmosphere, unite in the spot because of the cooling produced by expansion in the vortex.]

Astronomical observations of this character, it should be noted, are most effective when constantly tested and interpreted by laboratory experiment. Indeed, a modern astrophysical observatory should be equipped like a great physical laboratory, provided on the one hand with telescopes and accessory apparatus of the greatest attainable power, and on the other with every device known to the investigator of radiation and the related physical and chemical phenomena. Its telescopes, especially designed with the aims of the physicist and chemist in view, bring images of sun, stars, nebulae, and other heavenly bodies within the reach of powerful spectroscopes, sensitive bolometers and thermopiles, and the long array of other appliances available for the measurement and a.n.a.lysis of radiation. Its electric furnaces, arcs, sparks, and vacuum tubes, its apparatus for increasing and decreasing pressure, varying chemical conditions, and subjecting luminous gases and vapors to the influence of electric and magnetic fields, provide the means of imitating celestial phenomena, and of repeating and interpreting the experiments observed at the telescope.

And the advantage thus derived, as we have seen, is not confined to the astronomer, who has often been able, by making fundamental physical and chemical discoveries, to repay his debt to the physicist and chemist for the apparatus and methods which he owes to them.

NEWTON AND EINSTEIN

Take, for another example, the greatest law of physics--Newton's law of gravitation. Huge b.a.l.l.s of lead, as used by Cavendish, produce by their gravitational effect a minute rotation of a delicately suspended bar, carrying smaller b.a.l.l.s at its extremities. But no such feeble means sufficed for Newton's purpose. To prove the law of gravitation he had recourse to the tremendous pull on the moon of the entire ma.s.s of the earth, and then extended his researches to the mutual attractions of all the bodies of the solar system.

Later Herschel applied this law to the suns which const.i.tute double stars, and to-day Adams observes from Mount Wilson stars falling with great velocity toward the centre of the galactic system under the combined pull of the millions of objects that compose it. Thus full advantage has been taken of the possibility of utilizing the great ma.s.ses of the heavenly bodies for the discovery and application of a law of physics and its reciprocal use in explaining celestial motions.

[Ill.u.s.tration: Fig. 38. The Cavendish experiment.

Two lead b.a.l.l.s, each two inches in diameter, are attached to the ends of a torsion rod six feet long, which is suspended by a fine wire. The experiment consists in measuring the rotation of the suspended system, caused by the gravitational attraction of two lead spheres, each twelve inches in diameter, acting on the two small lead b.a.l.l.s.]

Or consider the Einstein theory of relativity, the truth or falsity of which is no less fundamental to physics. Its inception sprang from the Michelson-Morley experiment, made in a laboratory in Cleveland, which showed that motion of the earth through the ether of s.p.a.ce could not be detected. All of the three chief tests of Einstein's general theory are astronomical--because of the great ma.s.ses required to produce the minute effects predicted: the motion of the perihelion of Mercury, the deflection of the light of a star by the attraction of the sun, and the s.h.i.+ft of the lines of the solar spectrum toward the red--questions not yet completely answered.

But it is in the study of the const.i.tution of matter and the evolution of the elements, the deepest and most critical problem of physics and chemistry, that the extremes of pressure and temperature in the heavenly bodies, and the prevalence of other physical conditions not yet successfully imitated on earth, promise the greatest progress.