Practical Talks by an Astronomer — The Sun's Destination

We shall limit our extracts from the contemporary press to the few quotations here given, hoping that enough has been said to direct attention once more to that important subject, the Possibility of Being Deceived.

THE SUN'S DESTINATION

Three generations of men have come and gone since the Marquis de Laplace stood before the Academy of France and gave his demonstration of the permanent stability of our solar system.

There was one significant fault in Newton's superbly simple conception of an eternal law governing the world in which we live.

The labors of mathematicians following him had shown that the planets must trace out paths in space whose form could be determined in advance with unerring certainty by the aid of Newton's law of gravitation.

But they proved just as conclusively that these planetary orbits, as they are called, could not maintain indefinitely the same shapes or positions.

Slow indeed might be the changes they were destined to undergo; slow, but sure, with that sureness belonging to celestial science alone.

And so men asked: Has this magnificent solar system been built upon a scale so grand, been put in operation subject to a law sublime in its very simplicity, only to change and change until at length it shall lose every semblance of its former self, and end, perhaps, in chaos or extinction?

Laplace was able to answer confidently, "No." Nor was his answer couched in the enthusiastic language of unbalanced theorists who work by the aid of imagination alone.

Based upon the irrefragable logic of correct mathematical reasoning, and clad in the sober garb of mathematical formulæ, his results carried conviction to men of science the world over.

So was it demonstrated that changes in our solar system are surely at work, and shall continue for nearly countless ages; yet just as surely will they be reversed at last, and the system will tend to return again to its original form and condition.

The objection that the Newtonian law meant ultimate dissolution of the world was thus destroyed by Laplace.

From that day forward the law of gravitation has been accepted as holding sway over all phenomena visible within our planetary world.

The intricacies of our own solar system being thus illumined, the restless activity of the human intellect was stimulated to search beyond for new problems and new mysteries.

Even more fascinating than the movements of our sun and planets are all those questions that relate to the clustered stellar congeries hanging suspended within the deep vault of night.

Does the same law of gravitation cast its magic spell over that hazy cloud of Pleiades, binding them, like ourselves, with bonds indissoluble?

Who shall answer, yes or no?

We can only say that astronomers have as yet but stepped upon the threshold of the universe, and fixed the telescope's great eye upon that which is within.

Let us then begin by reminding the reader what is meant by the Newtonian law of gravitation.

It appears all things possess the remarkable property of attracting or pulling each other.

Newton declared that all substances, solid, liquid, or even gaseous--from the massive cliff of rock down to the invisible air--all matter can no more help pulling than it can help existing.

His law further formulates certain conditions governing the manner in which this gravitational attraction is exerted; but these are mere matters of detail; interest centres about the mysterious fact of attraction itself.

How can one thing pull another with no connecting link through which the pull can act?

Just here we touch the point that has never yet been explained.

Nature withholds from science her ultimate secrets.

They that have pondered longest, that have descended farthest of all men into the clear well of knowledge, have done so but to sound the depths beyond, never touching bottom.

This inability of ours, to give a good physical explanation of gravitation, has led certain makers of paradoxes to doubt or even deny that there is any such thing.

But, fortunately, we have a simple laboratory experiment that helps us.

Unexplained it may ever remain, but that there can be attraction between physical objects connected by no visible link is proved by the behavior of an ordinary magnet.

Place a small piece of steel or iron near a magnetized bar, and it will at once be so strongly attracted that it will actually fly to the magnet.

Anyone who has seen this simple experiment can never again deny the possibility, at least, of the law of attraction as stated by Newton.

Its possibility once admitted, the fact that it can predict the motions of all the planets, even down to their minutest details, transforms the possibility of its truth into a certainty as strong as any human certainty can ever be.

But this demonstration of Newton's law is limited strictly to the solar system itself.

We may, indeed, reason by analogy, and take for granted that a law which holds within our immediate neighborhood is extremely likely to be true also of the entire visible universe.

But men of science are loath to reason thus; and hence the fascination of researches in cosmic astronomy.

Analogy points out the path.

The astronomer is not slow to follow; but he seeks ever to establish upon incontrovertible evidence those truths which at first only his daring imagination had led him to half suspect.

If we are to extend the law of gravitation to the utmost, we must be careful to consider the law itself in its most complete form.

A heavenly body like the sun is often said to govern the motions of its family of planets; but such a statement is not strictly accurate.

The governing body is no despot; 'tis an abject slave of law and order, as much as the tiniest of attendant planets.

The action of gravitation is mutual, and no cosmic body can attract another without being itself in turn subject to that other's gravitational action.

If there were in our solar system but two bodies, sun and planet, we should find each one pursuing a path in space under the influence of the other's attraction.

These two paths or orbits would be oval, and if the sun and planet were equally massive, the orbits would be exactly alike, both in shape and size.

But if the sun were far larger than the planet, the orbits would still be similar in form, but the one traversed by the larger body would be small.

For it is not reasonable to expect a little planet to keep the big sun moving with a velocity as great as that derived by itself from the attraction of the larger orb.

Whenever the preponderance of the larger body is extremely great, its orbit will be correspondingly insignificant in size.

This is in fact the case with our own sun.

So massive is it in comparison with the planets that the orbit is too small to reveal its actual existence without the aid of our most refined instruments.

The path traced out by the sun's centre would not fill a space as large as the sun's own bulk.

Nevertheless, true orbital motion is there.

So we may conclude that as a necessary consequence of the law of gravitation every object within the solar system is in motion.

To say that planets revolve about the sun is to neglect as unimportant the small orbit of the sun itself.

This may be sufficiently accurate for ordinary purposes; but it is unquestionably necessary to neglect no factor, however small, if we propose to extend our reasoning to a consideration of the stellar universe.

For we shall then have to deal with systems in which the planets are of a size comparable with the sun; and in such systems all the orbits will also be of comparatively equal importance.

Mathematical analysis has derived another fact from discussion of the law of gravitation which, perhaps, transcends in simple grandeur everything we have as yet mentioned.

It matters not how great may be the number of massive orbs threading their countless interlacing curved paths in space, there yet must be in every cosmic system one single point immovable.

This point is called the Centre of Gravity.

If it should so happen that in the beginning of things, some particle of matter were situated at this centre, then would that atom ever remain unmoved and imperturbable throughout all the successive vicissitudes of cosmic evolution.

It is doubtful whether the mind of man can form a conception of anything grander than such an immovable atom within the mysterious intricacies of cosmic motion.

But in general, we cannot suppose that the centres of gravity in the various stellar systems are really occupied by actual physical bodies.

The centre may be a mere mathematical point in space, situated among the several bodies composing the system, but, nevertheless, endowed, in a certain sense, with the same remarkable property of relative immobility.

Having thus defined the centre of gravity in its relation to the constituent parts of any cosmic system, we can pass easily to its characteristic properties in connection with the inter-relation of stellar systems with one another.

It can be proved mathematically that our solar system will pull upon distant stars just as though the sun and all the planets were concentrated into one vast sphere having its centre in the centre of gravity of the whole.

It is this property of the centre of gravity which makes it pre-eminently important in cosmic researches.

For, while we know that centre to be at rest relatively to all the planets in the system, it may, nevertheless, in its quality as a sort of concentrated essence of them all, be moving swiftly through space under the pull of distant stars.

In that case, the attendant bodies will go with it--but they will pursue their evolutions within the system, all unconscious that the centre of gravity is carrying them on a far wider circuit.

What is the nature of that circuit?

This question has been for many years the subject of earnest study by the clearest minds among astronomers.

The greatest difficulty in the way is the comparatively brief period during which men have been able to make astronomical observations of precision.

Space and time are two conceptions that transcend the powers of definition possessed by any man.

But we can at least form a notion of how vast is the extent of time, if we remember that the period covered by man's written records is registered but as a single moment upon the great revolving dial of heaven's dome.

One hundred and fifty years have elapsed since James Bradley built the foundations of modern sidereal astronomy upon his masterly series of observations at the Royal Observatory of Greenwich, in England.

Yet so slowly do the movements of the stars unroll themselves upon the firmament, that even to this day no one of them has been seen by men to trace out more than an infinitesimal fraction of its destined path through the voids of space.

Travellers upon a railroad cannot tell at any given moment whether they are moving in a straight line, or whether the train is turning upon some curve of huge size.

The St. Gothard railway has several so-called "corkscrew" tunnels, within which the rails make a complete turn in a spiral, the train finally emerging from the tunnel at a point almost vertically over the entrance.

In this way the train is lifted to a higher level.

Passengers are wont to amuse themselves while in these tunnels by watching the needle of an ordinary pocket-compass.

This needle, of course, always points to the north; and as the train turns upon its curve, the needle will make a complete revolution.

But the passenger could not know without the compass that the train was not moving in a perfectly straight line.

Just so we passengers on the earth are unaware of the kind of path we are traversing, until, like the compass, the astronomer's instruments shall reveal to us the truth.

But as we have seen, astronomical observations of precision have not as yet extended through a period of time corresponding to the few minutes during which the St. Gothard traveller watches the compass.

We are still in the dark, and do not know as yet whether mankind shall last long enough upon the earth to see the compass needle make its revolution.

We are compelled to believe that the motion in space of our sun is progressing upon a curved path; but so far as precise observations allow us to speak, we can but say that we have as yet moved through an infinitesimal element only of that mighty curve.

However, we know the point upon the sky toward which this tiny element of our path is directed, and we have an approximate knowledge of the speed at which we move.

More than a century ago Sir William Herschel was able to fix roughly what we call the apex of the sun's way in space, or the point among the stars toward which that way is for the moment directed.

We say for the moment, but we mean that moment of which Bradley saw the beginning in 1750, and upon whose end no man of those now living shall ever look.

Herschel found that a comparison of old stellar observations seemed to indicate that the stars in a certain part of the sky were opening out, as it were, and that the constellations in the opposite part of the heavens seemed to be drawing in, or becoming smaller.

There can be but one reasonable explanation of this.

We must be moving toward that part of the sky where the stars are separating.

Just so a man watching a regiment of soldiers approaching, will see at first only a confused body of men; but as they come nearer, the individual soldiers will seem to separate, until at length each one is seen distinct from all the others.

Herschel fixed the position of the apex at a point in the constellation Hercules.

The most recent investigations of Newcomb and others have, on the whole, verified Herschel's conclusions.

With the intuitive power of rare genius, Herschel had been able to sift truth out of error.

The observational data at his disposal would now be called rude, but they disclosed to the scrutiny of his acute understanding the germ of truth that was in them.

Later investigators have increased the precision of our knowledge, until we can now say that the present direction of the solar motion is known within very narrow limits.

A tiny circle might be drawn on the sky, to which an astronomer might point his hand and say: "Yonder little circle contains the goal toward which the sun and planets are hastening to-day."

Even the speed of this motion has been subjected to measurement, and found to be about ten miles per second.

The objective point and the rate of motion thus stated, exact science holds her peace.

Here genuine knowledge stops; and we can proceed further only by the aid of that imagination which men of science need to curb at every moment.

But let no one think that the sun will ever reach the so-called apex.

To do so would mean cosmic motion upon a straight line, while every consideration of celestial mechanics points to motion upon a curve.

When shall we turn sufficiently upon that curve to detect its bending?

'Tis a problem we must leave as a rich heritage to later generations that are to follow us.

The visionary theorist's notion of a great central sun, controlling our own sun's way in space, must be dismissed as far too daring.

But for such a central sun we may substitute a central centre of gravity belonging to a great system of which our sun is but an insignificant member.

Then we reach a conception that has lost nothing in the grandeur of its simplicity, and is yet in accord with the probabilities of sober mechanical science.

We cease to be a lonely world, and stretch out the bonds of a common relationship to yonder stars within the firmament.

INDEX

PAGE

Airy, Astronomer Royal, 1 Allis, photographs comet, 101 Andromeda nebula, 28 temporary star, 28, 29, 45 Apex, of solar motion, explained, 221 Aquila, constellation, temporary star in, 40 Arctic regions, position of pole in, 194 Argo, constellation, variable star in, 205 Association, international geodetic, 139 Asteroids, first discovery by Piazzi, 59, 106 discovery by photography, 64 group of, 63 photography of, invented by Wolf, 104 Astronomer, royal, 1 working, description of, 152 ASTRONOMER'S POLE, THE, 184

Astronomy, journalistic, 176 practical uses of, 112 Atmospheric refraction, explained, 193 Axis, of figure of the earth, 136 of rotation of the earth, 136 polar, of telescope, 173 Barnard, discovers satellite of Jupiter, 51 Bessel, measures Pleiades, 15 Bond, discovers crape ring of Saturn, 144 Bradley, observes at Greenwich, 219 Brahe, Tycho, his temporary star, 40 Bruce, endows polar photography, 197 Campbell, observes Pole-star, 18 Cape of Good Hope, observatory, photography at, 101 telescope, 170, 174 _Capriccio_, Galileo's, 55 Cassini, shows Saturn's rings to be double, 144 Cassiopeia, temporary star in, 40 Celestial pole, 184 Central sun theory, 223 Centre of gravity, 217 Chart-room, on ship-board, 5 Chronometer, invention of, 8 Circle, meridian, explained, 189 Clerk Maxwell, discusses Saturn's rings, 146 Clock, affected by temperature, 117 affected by barometric pressure, 117 astronomical, 115 astronomical, how mounted, 116 astronomical, its dial, 116 error of, determined with transit, 118 jeweller's regulator, 114 of telescope, 175 Clusters of stars, photography of, 98 Columbia University Observatory, latitude observations, 139 polar photography, 196 Common, his reflecting telescope, 32 Confusion of dates, in Pacific Ocean, 125 Congress of Astronomers, Paris, 1887, 102 Constellations, 162 Control, "mouse," for photography, 88 Copernican theory of universe, 53, 56 demonstration, 94 Corkscrew tunnels, 220 Crape ring of Saturn, 144 Cumulative effect, in photography, 84 Date, confusion of, in Pacific Ocean, 125 Date-line, international, explained, 126 Development of photograph, 81 Dial, of astronomical clock, 116 "Dialogue" of Galileo, 53 Differences of time, explained, 121 Directions, telescopic measurement of, 21 Directory of the heavens, 103 Distance, of light-source in photography, 83 of stars, 94, 106, 158 of Sun, 67, 97, 106 Donner, polar photography, 195 Double telescopes, for photography, 86 Earth, motions of its pole, 131 rotation of, 136, 162, 171, 184 shape of, 135 Eclipses, photography of, 109 Elkin, measures Pleiades, 15 Equatorial telescope, explained, 170 Eros, discovered by Witt, 66, 105 its importance, 67 Error of clock, determined by transit, 118 Exposure, length of, in photography, 84 Feldhausen, Herschel's observatory near Capetown, 204 Fiji Islands, their date, 126 Fixed polar telescope, 197 "Following" the stars, 88, 173 Four-day cycle of pole-star, 24 France, outside time-zone system, 129 Fundamental longitude meridian, 124 GALILEO, 47

and the Church, 48 discoveries of, 49 observes Saturn, 141 Galle, discovers Neptune, 61 Gauss, computes first asteroid orbit, 60 Gautier, Paris, constructs big telescope, 179 Geodetic Association, international, 139 Geography, maps, astronomical side of, 112 Geology, polar motion in, 131 Gill, photographs comet, 100 Gilliss, at Naval Observatory, Washington, 169 Goldsborough, at Naval Observatory, Washington, 169 _Grande Lunette_, Paris, 1900, 176, 180 Gravitation, 13 in Pleiades, 14, 212 law of, Newton's, 212 Gravity, centre of, 217 Greenwich, origin of longitudes, 7, 124 time, 7 Groombridge, English astronomer, 1 Harrison, inventor of chronometer, 8 Head, of heliometer, 156 Heidelberg, photography at, 104 HELIOMETER, 152

head of, 156 how used, 157 principle of, 154 scales of, 158 semi-lenses of, 155 Helsingfors observatory, polar photography at, 195 Henry, measures Pleiades, 11, 17 Hercules, constellation, solar motion toward, 222 Herschel, discovers apex of solar motion, 221 discovers Uranus, 59, 141 John, the moon hoax, 200 Hipparchus, discovers precession, 186 early star-catalogue, 21, 39 invents star magnitudes, 91 Huygens, announces rings of Saturn, 142 his logogriph, 143 Ice-cap, of Earth, 131 _Index Librorum Prohibitorum_, 53 International, date-line, explained, 126 geodetic association, 139 Inter-stellar motion, in clusters, 98 in Pleiades, 14 Islands of Pacific, their longitude and time, 125 Japan, latitude station in, 139 Jewellers' correct time, 121 Journalistic astronomy, 176 Jupiter's satellites, discovered by Galileo, 50 discovered by Barnard, 51 Keeler, observes Saturn's rings, 140, 147, 150 photographs nebulæ, 32 "Keyhole" nebula, 205 Lambert, determines longitude of Washington, 168 Laplace, discusses Saturn's rings, 146 nebular hypothesis, 33 stability of solar system, 210 Latitude, changes of, 133, 138 definition of, 134 determining the, 6 Leverrier, predicts discovery of Neptune, 61, 142 Lick Observatory, Keeler's observations, 140 Light, undulatory theory of, 19, 148 Light-waves, measuring length of, 20, 149 Logogriph, by Huygens, 143 Long-exposure photography, 85 Longitude, counted East and West, 125 determining, 6 determining by occultations, 167 effect on time differences, 123 explained, 123 of Washington, first determined, 168 Maclear, observes Eta Argus, 205 Magnitudes, stellar, 91 Manila, its time, 127 Maps, astronomical side of, 112 Meridian circle, explained, 189 Milky-way, poor in nebulæ, 33 Minor Planets, see Asteroids.

MOON, HOAX, 199

motion among stars, 163 mountains discovered by Galileo, 49 size of, measured, 166 Motion of moon, 163 MOTIONS of the EARTH'S Pole, 131 MOUNTING GREAT TELESCOPES, 170

Naked-eye nebulæ, 28 Naples, Royal Observatory, latitude observations, 139 Naval Observatory, Washington, noon signal, 120 NAVIGATION, 1

before chronometers, 3 use of astronomy in, 113 NEBULÆ, 27

Nebula, in Andromeda, 28 in Orion, 30 "keyhole", 205 Nebular, hypothesis, 33 structure in Pleiades, 17 Nebulous stars, 31 Negative, and positive, in photography, 82 Neptune, discovery predicted by Leverrier, 61, 142 discovery by Galle, 61 Newcomb, fixes apex of solar motion, 222 Newton, law of gravitation, 212 longitude commission, 8 New York, its telegraphic time system, 120 Noon Signal, Washington, 120 Number, of nebulæ, 31, 33 of temporary stars, 38 Nutation, explained, 188 Occultations, 161 explained, 165 Occultations, use of, 166, 167 Orion nebula, 30 Pacific islands, their longitude and time, 125 Parallax, solar, 67, 106 stellar, 94, 106 measured with heliometer, 158 Paris, congress of astronomers, 1887, 102 exposition of 1900, 176 Periodic motion of earth's pole, 133 Perseus, constellation, temporary star in, 46 Philippine Islands, their time, 127 Photography, asteroid, invented by Wolf, 104 congress of astronomical, 102 cumulative effect of light, 84 distance of light-source, 83 double telescopes for, 86 general star-catalogue, 102 IN ASTRONOMY, 81

in discovery of asteroids, 64, 104 in solar physics, 109 in spectroscopy, 108 length of exposure, 84 measuring-machine, Rutherfurd, 93 motion of telescope for, 87 "mouse" control of telescope, 88 of eclipses, 109 of inter-stellar motion, 99 Paris congress, 1877, 102 polar, 191 Rutherfurd pioneer in, 90 star-clusters, 98 star-distances measured by, 94 summarized, 110 wholesale methods in, 103 Piazzi, discovers first asteroid, 59, 106 Pitkin, report to House of Representatives, 168 Planetary nebulæ, 31 PLANET OF 1898, 58

Planetoids, see Asteroids.

Planets known to ancients, 58 PLEIADES, 10

gravitation among, 212 motion among, 14, 16, 98 nebular structure, 17 number visible, 11 Polar axis, of telescope, 173 Polar photography, 191 at Helsingfors, 195 Pole, celestial, 184 of the earth, motions of, 131 THE ASTRONOMER'S, 184

POLE-STAR, 18

as a binary, 25 as a triple, 18, 26 change of, 187 its four-day cycle, 24 motion toward us, 24 Positive, and negative, in photography, 82 Potsdam, observatory, photographic star-catalogue, 103 Practical uses of astronomy, 112 Precession, explained, 186 Prize, for invention of chronometer, 8 Ptolemaic theory of universe, 56 Ptolemy, writes concerning Hipparchus, 39 Railroad time, explained, 127 Refraction, atmospheric, explained, 193 "Regulator," the jeweller's clock, 114 Ring-nebulæ, 31 Rings, of Saturn, see Saturn's rings.

Roberts, Andromeda nebula, 28 Rotation, of Earth, 136, 162, 171, 184 of Saturn, 150 Royal Astronomer, his duties, 2 Royal Observatory, Greenwich, 124 Greenwich, Bradley's observations, 219 Naples, latitude observations, 139 Rutherfurd, cluster photography, 99 invents photographic apparatus, 93 pioneer in photography, 90 stellar parallax, 94 Sagredus, character in Galileo's Dialogue, 55 Salusbury, Galileo's translator, 50, 54 Salviati, character in Galileo's Dialogue, 55 Samoa, its date, 126 SATURN'S RINGS, 140

analogy to planetoids, 147 announced by Huygens, 142 observed with spectroscope, 147 shown to be double by Cassini, 144 structure and stability, 145 Scales, of heliometer, 158 Scorpio, constellation, temporary star in, 39 Semi-lenses of heliometer, 155 Sextant, how used, 4 Sicily, latitude station in, 139 _Sidereus Nuncius_, published by Galileo, 52 Simplicio, character in Galileo's Dialogue, 55 Sirius, brightest star, 205 Size of Moon, measured, 166 _Société de l'Optique_, 177 Solar parallax, see Sun's distance.

physics, by photography, 109 system, stability of, 210 Spectroscope, its use explained, 147 used on pole-star, 19 to observe Saturn's rings, 147 Spiral nebulæ, 31 Stability, of Saturn's rings, 145 of Solar System, 210 Standards, time, of the world, 111 table of, 130 "Standard" time, explained, 127 Star-catalogue, general photographic, 102 Star-clusters, photography of, 98 Star-distances 94, 106 measured with heliometer, 158 Rutherfurd, 94 Star magnitudes, 91 Star-motion, toward us, 21 Star-tables, astronomical, 118 Stars, variable, 42 St Gothard railway, tunnels, 220 Sun, newspaper, the moon hoax, 201 SUN-DIAL, HOW TO MAKE A, 69

SUN'S, DESTINATION, 210

distance, compared with star distance, 97 measured with Eros, 67, 106 motion, apex of, 221 Sun-spots, discovered by Galileo, 49 _Systema Saturnium_, Huygens, 143 Telescope, clock, 175 at Paris Exposition, 176, 180 double, for photography, 86 equatorial, explained, 170 first used by Galileo, 49 motion of, 87 mounting great, 170 unmoving, for polar photography, 197 TEMPORARY STARS, 37

in Andromeda nebula, 28, 29, 45 in Aquila, 40 in Cassiopeia, 40 in Perseus, 46 in Scorpio, 39 their number, 38 theory of, 42 Time, correct, determined astronomically, 113 differences between different places, 121 TIME STANDARDS OF THE WORLD, 111

standards of the World, table of, 130 system, in New York, 120 zones, explained, 128 Trails, photographic, 191 Transit, for determining clock error, 118 Tycho Brahe, his temporary star, 40 Ulugh Beg, early star-catalogue, 21 Undulatory theory, of light, 19, 148 Universe, theories of, 34, 53, 56 Uranus, discovered by Herschel, 59, 142 Use of occultations, 166, 167 Uses of astronomy, practical, 112 Variable stars, 42 in Argo, 205 Vega, future pole-star, 187 Visibility of stars, in day-time, 191 Vision, phenomenon of, 20, 149 Washington, its longitude first determined, 168 Waves, explained, 148 of light, 20, 148 Wilkes, at Naval Observatory, Washington, 169 Wilkins, imaginary voyage of, 208 Witt, discovers Eros, 66, 105 Wolf, M, invents asteroid photography, 104 measures Pleiades, 11 World's time standards, table of, 130 Yale College, Pleiades measured at, 15 Zones, time, explained, 128 TRANSCRIBER'S NOTE

Italic text is denoted by _underscores_.

Fractions in the two tables on pg 74 and pg 78 are displayed in the form "a-b/c" as 4-1/2 or 2-7/16 for example.

The original text in the tables used the form "a b-c".

A few other basic fractions in the text such as ½ and ⅖ are displayed in this same form in the etext.

There is only one Footnote in this book, with its anchor on pg 69. It has been placed at the end of the chapter containing the anchor.

Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources.

Except for those changes noted below, all misspellings in the text, and inconsistent or archaic usage, have been retained.

For example, time zone, time-zone; Le Verrier, Leverrier; light wave, light-wave;

intrust; wabbling; unexcelled; crape; monumented.

Pg 146, 'James Clark-Maxwell' replaced by 'James Clerk Maxwell'.

Pg 189, 'impossible to measure' replaced by 'possible to measure'.

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