Part 1

PLEASANT WAYS IN SCIENCE.

WORKS BY RICHARD A. PROCTOR.

LIGHT SCIENCE FOR LEISURE HOURS: Familiar Essays on Scientific Subjects. Crown 8vo, 3_s._ 6_d._

THE ORBS AROUND US: A Series of Essays on the Moon and Planets, Meteors and Comets. With Charts and Diagrams. Crown 8vo, 3_s._ 6_d._

OTHER WORLDS THAN OURS: The Plurality of Worlds Studied under the Light of Recent Scientific Researches. With 14 Illustrations. Crown 8vo, 3_s._ 6_d._

OTHER SUNS THAN OURS: A Series of Essays on Suns—Old, Young, and Dead. With other Science Gleanings. Two Essays on Whist, and Correspondence with Sir John Herschel. With 9 Star Maps and Diagrams. Cr. 8vo, 3_s._ 6_d._

THE MOON: Her Motions, Aspects, Scenery, and Physical Condition. With Plates, Charts, Woodcuts, &c. Crown 8vo, 3_s._ 6_d._

UNIVERSE OF STARS: Presenting Researches into and New Views respecting the Constitution of the Heavens. With 22 Charts and 22 Diagrams. 8vo, 10_s._ 6_d._

LARGER STAR ATLAS for the Library, in 12 Circular Maps, with Introduction and 2 Index Pages. Folio, 15_s._; or Maps only, 12_s._ 6_d._

NEW STAR ATLAS for the Library, the School, and the Observatory, in 12 Circular Maps. Crown 8vo, 5_s._

HALF-HOURS WITH THE STARS: A Plain and Easy Guide to the Knowledge of the Constellations. Showing in 12 Maps the position of the principal Star Groups night after night throughout the Year. With Introduction and a separate Explanation of each Map. True for every Year. 4to, 3_s._ net.

HALF-HOURS WITH THE TELESCOPE: A Popular Guide to the Use of the Telescope as a means of Amusement and Instruction. With 7 Plates. Fcp. 8vo, 2_s._ 6_d._

THE STARS IN THEIR SEASONS: An Easy Guide to a Knowledge of the Star Groups, in 12 Large Maps. Imperial 8vo, 5_s._

THE SOUTHERN SKIES: A Plain and Easy Guide to the Constellations of the Southern Hemisphere. Showing in 12 Maps the position of the principal Star Groups night after night throughout the Year. With an Introduction and a separate Explanation of each Map. True for every Year. 4to, 5_s._

STAR PRIMER: Showing the Starry Sky Week by Week, in 24 Hourly Maps. Crown 4to, 2_s._ 6_d._

ROUGH WAYS MADE SMOOTH: Familiar Essays on Scientific Subjects. Crown 8vo, 3_s._ 6_d._

OUR PLACE AMONG INFINITIES: A Series of Essays contrasting our Little Abode in Space and Time with the Infinities around us. Crown 8vo, 3_s._ 6_d._

THE EXPANSE OF HEAVEN: Essays on the Wonders of the Firmament. Crown 8vo, 3s. 6_d._

THE GREAT PYRAMID: OBSERVATORY, TOMB, AND TEMPLE. With Illustrations. Crown 8vo, 5_s._

PLEASANT WAYS IN SCIENCE. Crown 8vo, 3_s._ 6_d._

MYTHS AND MARVELS OF ASTRONOMY. Crown 8vo, 3_s._ 6_d._

NATURE STUDIES. By GRANT ALLEN, A. WILSON, T. FOSTER, E. CLODD, and R. A. PROCTOR. Crown 8vo, 3_s._ 6_d._

LEISURE READINGS. By E. CLODD, A. WILSON, T. FOSTER, A. C. RANYARD, and R. A. PROCTOR. Crown 8vo, 5_s._ Cheap Edition, 3_s._ 6_d._

STRENGTH: How to Get Strong and Keep Strong. With Chapters on Rowing and Swimming, Fat, Age, and the Waist. With 9 Illustrations. Crown 8vo, 2_s._

CHANCE AND LUCK: A Discussion of the Laws of Luck, Coincidences, Wagers, Lotteries, and the Fallacies of Gambling, &c. Crown 8vo, 2_s._ 6_d._

HOW TO PLAY WHIST: With the Laws and Etiquette of Whist. Crown 8vo, 3_s._ net.

HOME WHIST: An Easy Guide to Correct Play. 16mo, 1_s._

LONDON: LONGMANS, GREEN, & CO.

PLEASANT WAYS IN SCIENCE

BY RICHARD A. PROCTOR

AUTHOR OF “ROUGH WAYS MADE SMOOTH,” “THE EXPANSE OF HEAVEN,” “OUR PLACE AMONG INFINITIES,” “MYTHS AND MARVELS OF ASTRONOMY,” ETC. ETC.

_NEW IMPRESSION_

LONGMANS, GREEN, AND CO. 39 PATERNOSTER ROW, LONDON NEW YORK AND BOMBAY 1905

CONTENTS.

PAGE OXYGEN IN THE SUN 1

SUN-SPOT, STORM, AND FAMINE 28

NEW WAYS OF MEASURING THE SUN’S DISTANCE 56

DRIFTING LIGHT WAVES 77

THE NEW STAR WHICH FADED INTO STAR-MIST 106

STAR-GROUPING, STAR-DRIFT, AND STAR-MIST 136

MALLET’S THEORY OF VOLCANOES 151

TOWARDS THE NORTH POLE 156

A MIGHTY SEA-WAVE 178

STRANGE SEA CREATURES 199

ON SOME MARVELS IN TELEGRAPHY 232

THE PHONOGRAPH, OR VOICE-RECORDER 274

THE GORILLA AND OTHER APES 296

THE USE AND ABUSE OF FOOD 330

OZONE 347

DEW 357

THE LEVELLING POWER OF RAIN 367

ANCIENT BABYLONIAN ASTROGONY 388

PREFACE.

It is very necessary that all who desire to become really proficient in any department of science should follow the beaten track, toiling more or less painfully over the difficult parts of the high road which is their only trustworthy approach to the learning they desire to attain. But there are many who wish to learn about scientific discoveries without this special labour, for which some have, perhaps, little taste, while many have scant leisure. My purpose in the present work, as in my “Light Science for Leisure Hours,” the “Myths and Marvels of Astronomy,” the “Borderland of Science,” and “Science Byways,” has been to provide paths of easy access to the knowledge of some of the more interesting discoveries, researches, or inquiries of the science of the day. I wish it to be distinctly understood that my purpose is to interest rather than to instruct, in the strict sense of the word. But I may add that it seems to me even more necessary to be cautious, and accurate in such a work as the present than in advanced treatises. For in a scientific work the reasoning which accompanies the statements of fact affords the means of testing and sometimes of correcting such statements. In a work like the present, where explanation and description take the place of reasoning, there is no such check. For this reason I have been very careful in the accounts which I have given of the subjects here dealt with. I have been particularly careful not to present, as established truths, such views as are at present only matters of opinion.

The essays in the present volume are taken chiefly from the _Contemporary Review_, the _Gentleman’s Magazine_, the _Cornhill Magazine_, _Belgravia_, and _Chambers’ Journal_. The sixth, however, presents the substance (and official report) of a lecture which I delivered at the Royal Institution in May, 1870. It was then that I first publicly enunciated the views respecting the stellar universe which I afterwards more fully stated in my “Universe of Stars.” The same views have also been submitted to the Paris Academy of Science, as the results of his own investigations, by M. Flammarion, in words which read almost like translations of passages in the above-mentioned essay.

RICHARD A. PROCTOR.

PLEASANT WAYS IN SCIENCE.

_OXYGEN IN THE SUN._

The most promising result of solar research since Kirchhoff in 1859 interpreted the dark lines of the sun’s spectrum has recently been announced from America. Interesting in itself, the discovery just made is doubly interesting in what it seems to promise in the future. Just as Kirchhoff’s great discovery, that a certain double dark line in the solar spectrum is due to the vapour of sodium in the sun’s atmosphere, was but the first of a long series of results which the spectroscopic analysis of the sun was to reveal, so the discovery just announced that a certain important gas—the oxygen present in our air and the chief chemical constituent of water—shows its presence in the sun by bright lines instead of dark, will in all probability turn out to be but the firstfruits of a new method of examining the solar spectrum. As its author, Dr. Henry Draper, of New York, remarks, further investigation in the direction he has pursued will lead to the discovery of other elements in the sun, but it was not “proper to conceal, for the sake of personal advantage, the principle on which such researches are to be conducted.” It may well happen, though I anticipate otherwise, that by thus at once describing his method of observation, Dr. Draper may enable others to add to the list of known solar elements some which yet remain to be detected; but if Dr. Draper should thus have added but one element to that list, he will ever be regarded as the physicist to whose acumen the method was due by which all were detected, and to whom, therefore, the chief credit of their discovery must certainly be attributed.

I propose briefly to consider the circumstances which preceded the great discovery which it is now my pleasing duty to describe, in order that the reader may the more readily follow the remarks by which I shall endeavour to indicate some of the results which seem to follow from the discovery, as well as the line along which, in my opinion, the new method may most hopefully be followed.

It is generally known that what is called the spectroscopic method of analyzing the sun’s substance had its origin in Kirchhoff’s interpretation of the dark lines in the solar spectrum. Until 1859 these dark lines had not been supposed to have any special significance, or rather it had not been supposed that their significance, whatever it might be, could be interpreted. A physicist of some eminence spoke of these phenomena in 1858 in a tone which ought by the way seldom to be adopted by the man of science. “The phenomena defy, as we have seen,” he said, “all attempts hitherto to reduce them within empirical laws, and no complete explanation or theory of them is possible. All that theory can be expected to do is this—it may explain how dark lines of any sort may arise within the spectrum.” Kirchhoff, in 1859, showed not only how dark lines of any sort may appear, but how and why they do appear, and precisely what they mean. He found that the dark lines of the solar spectrum are due to the vapours of various elements in the sun’s atmosphere, and that the nature of such elements may be determined from the observed position of the dark lines. Thus when iron is raised by the passage of the electric spark to so intense a degree of heat that it is vaporized, the light of the glowing vapour of iron is found to give a multitude of bright lines along the whole length of the spectrum—that is, some red, some orange, some yellow, and so on. In the solar spectrum corresponding dark lines are found along the whole length of the spectrum—that is, some in the red, some in the orange, yellow, etc., and precisely in those parts of these various spectral regions which the bright lines of glowing iron would occupy. Multitudes of other dark lines exist of course in the solar spectrum. But those corresponding to the bright lines of glowing iron are unquestionably there. They are by no means lost in the multitude, as might be expected; but, owing to the peculiarity of their arrangement, strength, etc., they are perfectly recognizable as the iron lines reversed, that is, dark instead of bright. Kirchhoff’s researches showed how this is to be interpreted. It means that the vapour of iron exists in the atmosphere of the sun, glowing necessarily with an intensely bright light; _but_, being cooler (however intensely hot) than the general mass of the sun within, the iron vapour absorbs more light than it emits, and the result is that the iron lines, instead of appearing bright, as they would if the iron vapour alone were shining, appear relatively dark on the bright rainbow-tinted background of the solar spectrum.

Thus was it shown that in the atmosphere of the sun there is the glowing vapour of the familiar metal, iron; and in like manner other metals, and one element (hydrogen) which is not ordinarily regarded as a metal, were shown to be present in the sun’s atmosphere. In saying that they are present in the sun’s atmosphere, I am, in point of fact, saying that they are present in the sun; for the solar atmosphere is, in fact, the outer part of the sun himself, since a very large part, if not by far the greater part, of the sun’s mass must be vaporous. But no other elements, except the metals iron, sodium, barium, calcium, magnesium, aluminium, manganese, chromium, cobalt, nickel, zinc, copper, and titanium, and the element hydrogen, were shown to be present in the sun, by this method of observing directly the solar dark lines. In passing, I may note that there are reasons for regarding hydrogen as a metallic element, strange though the idea may seem to those who regard hardness, brightness, malleability, ductility, plasticity, and the like, as the characteristic properties of metals, and necessarily fail to comprehend how a gas far rarer, under the same conditions, than the air we breathe, and which cannot possibly be malleable, ductile, or the like, can conceivably be regarded as a metal. But there is in reality no necessary connection between any one of the above properties and the metallic nature; many of the fifty-five metals are wanting in all of these properties; nor is there any reason why, as we have in mercury a metal which at ordinary temperatures is a liquid, so we might have in hydrogen a metal which, at all obtainable temperatures, and under all obtainable conditions of pressure, is gaseous. It was shown by the late Professor Graham (aided in his researches most effectively by Dr. Chandler Roberts) that hydrogen will enter into such combination with the metal palladium that it may be regarded as forming, for the time, with the palladium, an alloy; and as alloys can only be regarded as compounds of two or more metals, the inference is that hydrogen is in reality a metallic element.

Fourteen only of the elements known to us, or less than a quarter of the total number, were thus found to be present in the sun’s constitution; and of these all were metals, if we regard hydrogen as metallic. Neither gold nor silver shows any trace of its presence, nor can any sign be seen of platinum, lead, and mercury. But, most remarkable of all, and most perplexing, was the absence of all trace of oxygen and nitrogen, two gases which could not be supposed wanting in the substance of the great ruling centre of the planetary system. It might well be believed, indeed, that none of the five metals just named are absent from the sun, and indeed that every one of the forty metals not recognized by the spectroscopic method nevertheless exists in the sun. For according to the nebular hypothesis of the origin of our solar system, the sun might be expected to contain all the elements which exist in our earth. Some of these elements might indeed escape discovery, because existing only in small quantities; and others (as platinum, gold, and lead, for example), because but a small portion of their vaporous substance rose above the level of that glowing surface which is called the photosphere. But that oxygen, which constitutes so large a portion of the solid, liquid, and vaporous mass of our earth, should not exist in enormous quantities, and its presence be very readily discernable, seemed amazing indeed. Nitrogen, also, might well be expected to be recognizable in the sun. Carbon, again, is so important a constituent of the earth, that we should expect to discover clear traces of its existence in the sun. In less degree, similar considerations apply to sulphur, boron, silicon, and the other non-metallic elements.

It was not supposed, however, by any one at all competent to form an opinion on the subject, that oxygen, nitrogen, and carbon are absent from the sun. It was perceived that an element might exist in enormous quantities in the substance of the sun, and yet fail to give any evidence of its presence, or only give such evidence as might readily escape recognition. If we remember how the dark lines are really caused, we shall perceive that this is so. A glowing vapour in the atmosphere of the sun absorbs rays of the same colour as it emits. If then, it is cooler than the glowing mass of the sun which it enwraps, and if, notwithstanding the heat received from this mass, it remains cooler, then it suffers none of those rays to pass earthwards.[1] It emits rays of the same kind (that is, of the same _colour_) itself, but, being cooler, the rays thus coming from it are feebler; or, to speak more correctly, the ethereal waves thus originated are feebler than those of the same order which _would_ have travelled earthwards from the sun but for the interposed screen of vapour. Hence the corresponding parts of the solar spectrum are less brilliant, and contrasted with the rainbow-tinted streak of light, on which they lie as on a background, they appear dark.

In order, then, that any element may be detected by its dark lines, it is necessary that it should lie as a vaporous screen between the more intensely heated mass of the sun and the eye of the observer on earth. It must then form an enclosing envelope cooler than the sun within it. Or rather, some part of the vapour must be thus situated. For enormous masses of the vapour might be within the photospheric surface of the sun at a much higher temperature, which yet, being enclosed in the cooler vaporous shell of the same substance, would not be able to send its light rays earthwards. One may compare the state of things, so far as that particular element is concerned, to what is presented in the case of a metallic globe cooled on the outside but intensely hot within. The cool outside of such a globe is what determines the light and heat received from it, so long as the more heated mass within has not yet (by conduction) warmed the exterior shell. So in the case of a vapour permeating the entire mass, perhaps, of the sun, and at as high a temperature as the sun everywhere except on the outside: it is the temperature of the outermost part of such a vaporous mass which determines the intensity of the rays received from it—or in other words, determines whether the corresponding parts of the spectrum shall be darker or not than the rest of the spectrum. If the vapour does not rise above the photosphere of the sun in sufficient quantity to exercise a recognizable absorptive effect, its presence in the sun will not be indicated by any dark lines.

I dwell here on the question of quantity, which is sometimes overlooked in considering the spectroscopic evidence of the sun’s condition, but is in reality a very important factor in determining the nature of the evidence relating to each element in the solar mass. In some cases, the quantity of a material necessary to give unmistakable spectroscopic evidence is singularly small; insomuch that new elements, as thallium, cæsium, rubidium, and gallium, have been actually first recognized by their spectral lines when existing in such minute quantities in the substances examined as to give no other trace whatever of their existence. But it would be altogether a mistake to suppose that some element existing in exceedingly small quantities, or, more correctly, existing in the form of an exceedingly rare vapour in the sun’s atmosphere, would be detected by means of its dark lines, or _by any other method depending on the study of the solar spectrum_. When we place a small portion of some substance in the space between the carbon points of an electric lamp, and volatilize that substance in the voltaic arc, we obtain a spectrum including all the bright lines of the various elements contained in the substance; and if some element is contained in it in exceedingly small quantity, we may yet perceive its distinctive bright lines among the others (many of them far brighter) belonging to the elements present in greater quantities. But if we have (for example) a great mass of molten iron, the rainbow-tinted spectrum of whose light we examine from a great distance, and if a small quantity of sodium, or other substance which vaporizes at moderate temperatures, be cast into the molten iron so that the vapour of the added element presently rises above the glowing surface of the iron, no trace of the presence of this vapour would be shown in the spectrum observed from a distance. The part of the spectrum where the dark lines of sodium usually appear would, undoubtedly, be less brilliant than before, in the same sense that the sun may be said to be less brilliant when the air is in the least degree moist than when it is perfectly dry; but the loss of brilliancy is as utterly imperceptible in the one case as it is in the other. In like manner, a vapour might exist in the atmosphere of the sun (above the photosphere, that is), of whose presence not a trace would be afforded in the spectroscope, for the simple reason that the absorptive action of the vapour, though exerted to reduce the brightness of particular solar rays or tints, would not affect those rays sufficiently for the spectroscopist to recognize any diminution of their lustre.