Part 19 (1/2)
(see pp. 334, 335 of that book), it has been shown that these prominences are in rapid motion: at one moment they shoot up to heights of many thousand miles, at another they recede towards the centre of the sun.
We thus arrive at a picture of the solar atmosphere as consisting of layers of very hot gases, which are continually changing their relative positions and forms; sometimes ejections of intensely hot, glowing gases occur,--we call these prominences; sometimes down-rushes of gaseous matter occur,--we call these spots. Among the substances which compose the gaseous layers we recognize hydrogen, iron, magnesium, sodium, nickel, chromium, etc., but we also find substances which can at present be distinguished only by means of the wave-lengths of the light which they emit; thus we have 1474 stuff, 5017 stuff, 5369 stuff, etc.
Let us now turn to another part of this subject. By a special arrangement of apparatus it is possible to observe the spectrum of the light emitted by a glowing vapour, parts of which are hotter than other parts, and to compare the lines in the spectrum of the light coming from the hottest parts with the lines in the spectrum of the light coming from the cooler parts of the vapour. If this is done for sodium vapour, certain lines are apparent in all the spectra, others only in the spectrum of the light coming from the hottest parts of the sodium vapour: the former lines are called ”long lines,” the latter ”short lines.” A rough representation of the long and short lines of sodium is given in Fig. 7.
[Ill.u.s.tration: Fig. 7.--Long and short lines of sodium.]
Now, suppose that the lines in the spectrum of the light emitted by glowing manganese vapour have been carefully mapped, and cla.s.sed as long and short lines: suppose that the same thing has been done for the iron lines: now let a little manganese be mixed with much iron, let the mixture be vaporized, and let the light which is emitted be decomposed by the prism of a spectroscope, it will be found that the long lines of manganese alone make their appearance; let a little more manganese be added to the mixture, and now some of the shorter lines due to manganese begin to appear in the spectrum. Hence it has been concluded by Lockyer that if the spectrum of the light emitted by the glowing vapour of any element--call it A--is free from the long lines of any other element--say element B--this second element is not present as an impurity in the specimen of element A which is being examined. Lockyer has applied this conclusion to ”purify” various elementary spectra.
The spectrum of element A is carefully mapped, and the lines are divided into long and short lines, according as they are noticed in the spectrum of the light coming from all parts of the glowing vapour of A, or only in the spectrum of the light which comes from the hotter parts of that vapour. The spectra of elements B and C are similarly mapped and cla.s.sified: then the three spectra are compared; the longest line in the spectrum of B is noted, if this line is found in the spectrum of A, it is marked with a negative sign--this means that so far as the evidence of this line goes B is present as an impurity in A; the next longest B line is searched for in the spectrum of A--if present it also is marked with a negative sign; a similar process of comparison and elimination is conducted with the spectra of A and C. In this way a ”purified” spectrum of the light from A is obtained--a spectrum, that is, from which, according to Lockyer, all lines due to the presence of small quant.i.ties of B and C as impurities in A have been eliminated.
[Ill.u.s.tration: Fig. 8.]
Fig. 8 is given in order to make this ”purifying” process more clearly understood. But when this process has been completed there remain, in many cases, a few short lines common to two or more elementary spectra: such lines are called by Lockyer _basic lines_. He supposes that these lines are due to light emitted by forms of matter simpler than our elements; he thinks that at very high temperatures some of the elements are decomposed, and that the _bases_ of these elements are produced and give out light, which light is a.n.a.lyzed by the spectroscope. Such short basic lines are marked in the spectra represented in Fig. 8 with a positive sign.
Now, if the a.s.sumption made by Lockyer be admitted, viz. that the short lines, or some of the short lines, which are coincident in the ”purified”
spectra of various elements, are really due to light emitted by forms of matter into which our so-called elements are decomposed at very high temperatures, it follows that such lines should become more prominent in the spectra of the light emitted by elements the higher the temperature to which these elements are raised. But we know (see p. 308) that the prominences around the sun's disc are hotter than the average temperature of the solar atmosphere; hence the spectrum of the light coming from these prominences ought to be specially rich in ”basic” lines: this supposition is confirmed by experiment. Lockyer has also shown that it is the ”basic,”
and not the long lines, which are especially affected in the spectra of light coming from those parts of the solar atmosphere which are subjected to the action of cyclones, _i.e._ which are at abnormally high temperatures. And finally, a very marked a.n.a.logy has been established between the changes in the spectrum of the light emitted by a compound substance as the temperature is raised, and the substance is gradually decomposed into its elements, and the spectrum of the light emitted by a so-called elementary substance as the temperature of that substance is increased.
But it may be urged that Lockyer's method of ”purifying” a spectrum is not satisfactory; that, although all the longer lines common to two spectra are eliminated, the coincident short lines which remain are due simply to very minute quant.i.ties of one element present as an impurity in the larger quant.i.ty of the other. Further, it has been shown that several of the so-called ”basic” lines are resolved, by spectroscopes of great dispersive power, into groups of two or more lines, which lines are not coincident in different spectra.
And moreover it is possible to give a fairly satisfactory explanation of the phenomena of solar chemistry without the aid of the hypothesis that our elements are decomposed in the sun into simpler forms of matter.
Nevertheless this hypothesis has a certain amount of experimental evidence in its favour; it may be a true hypothesis. I do not think we are justified at present either in accepting it as the best guide to further research, or in wholly rejecting it.
The researches to which this hypothesis has given rise have certainly thrown much light on the const.i.tution of the sun and stars, and they have also been instrumental in forcing new views regarding the nature of the elements on the attention of chemists, and so of awakening them out of the slumber into which every cla.s.s of men is so ready to fall.
The tale told by the rays of light which travel to this earth from the sun and stars has not yet been fully read, but the parts which the chemist has spelt out seem to say that, although the forms of matter of which the earth is made are also those which compose the sun and stars, yet in the sun and stars some of the earthly elements are decomposed, and some of the earthly atoms are split into simpler forms. The tale, I say, told by the rays of light seems to bear this interpretation, but it is written in a language strange to the children of this earth, who can read it as yet but slowly; for the name given to the new science was ”_Ge-Urania_, because its production was of earth and heaven. And it could not taste of death, by reason of its adoption into immortal palaces; but it was to know weakness, and reliance, and the shadow of human imbecility; and it went with a lame gait; but in its going it exceeded all mortal children in grace and swiftness.”
There are certain little particles so minute that at least sixty millions of them are required to compose the smallest portion of matter which can be seen by the help of a good microscope. Some of these particles are vibrating around the edge of an orb a million times larger than the earth, but at a distance of about ninety millions of miles away. The student of science is told to search around the edge of the orb till he finds these particles, and having found them, to measure the rates of their vibrations; and as an instrument with which to do this he is given--a gla.s.s prism! But he has accomplished the task; he has found the minute particles, and he has measured their vibration-periods.
Chemistry is no longer confined to this earth: the chemist claims the visible universe as his laboratory, and the sunbeams as his servants.
Davy decomposed soda and potash by using the powerful instrument given him by Volta; but the chemist to-day has thrown the element he is seeking to decompose into a crucible, which is a sun or a star, and awaits the result.
The alchemists were right. There is a philosopher's stone; but that stone is itself a compound of labour, perseverance, and genius, and the gold which it produces is the gold of true knowledge, which shall never grow dim or fade away.
CHAPTER VIII.
SUMMARY AND CONCLUSION.
We have thus traced some of the main paths along which Chemistry has advanced since the day when, ceasing to be guided by the dreams of men who toiled with but a single idea in the midst of a world of strange and complex phenomena, she began to recognize that Nature is complex but orderly, and so began to be a branch of true knowledge.
In this review we have, I think, found that the remark made at the beginning of the introductory chapter is, on the whole, a just one. That the views of the alchemists, although sometimes very n.o.ble, were ”vague and fanciful” is surely borne out by the quotations from their writings given in the first chapter. This period was followed by that wherein the accurate, but necessarily somewhat narrow conception of the Lavoisierian chemistry prevailed. Founded for the most part on the careful, painstaking, and quant.i.tative study of one phenomenon--a very wide and far-reaching phenomenon, it is true--it was impossible that the cla.s.sification introduced by the father of chemical science should be broad enough to include all the discoveries of those who came after him. But although this cla.s.sification had of necessity to be revised and recast, the genius of Lavoisier enunciated certain truths which have remained the common possession of every chemical system. By proving that however the forms of matter may be changed the ma.s.s remains unaltered, he for the first time made a science of chemistry possible. He defined ”element” once for all, and thus swept away the fabric of dreams raised by the alchemists on the visionary foundation of _earth_, _air_, _fire_ and _water_, or of _mercury_, _sulphur_ and _salt_. By his example, he taught that weighings and measurements must be made before accurate knowledge of chemical reactions can be hoped for; and by his teaching about oxygen being _the acidifier_--although we know that this teaching was erroneous in many details--he showed the possibility of a system of cla.s.sification of chemical substances being founded on the actually observed properties and composition of those substances.
Lavoisier gained these most important results by concentrating his attention on a few subjects of inquiry. That chemistry might become broad it was necessary that it should first of all become narrower.
The period when the objects of the science were defined and some of its fundamental facts and conceptions were established, was succeeded, as we saw in our sketch, by that in which Dalton departed somewhat from the method of investigation adopted by most masters in science, and by concentrating his great mental powers on facts belonging to one branch of natural knowledge, elaborated a simple but very comprehensive theory, which he applied to explain the facts belonging to another branch of science.