shift about or dodge, and secondarily to alter a little, especially for the worse. His employment of the word zetetic is less doubtful; as he claims for his system that it alone is founded on the true seeking out of Nature's secrets.

The experimental basis of the theory of Parallax is mainly this: Having betaken himself to a part of the Bedford Canal, where there is an uninterrupted water-line of about six miles, he tested the water-surface for signs of curvature; and (so he said) found none.

It chanced, unfortunately, that a disciple-Mr. John Hampden, of Swindon -accepted the narrative of this observation in an unquestioning spirit; and was so confident that the Bedford Canal has a truly plane surface, that he wagered five hundred pounds on his opinion, challenging the believers in the earth's rotundity to repeat the experiment. The challenge was accepted by Mr. Wallace, the eminent naturalist; and the result may be anticipated. Three boats were to be moored in a line, three miles or so between each. Each carried a mast of given length. If, when the summits of the first and last masts were seen in a line through a telescope, the summit of the middle mast was not found to be above the line, then Mr. Hampden was to receive five hundred pounds from Mr.Wallace. If, on the contrary, the top of the middle mast was found, as the accepted theory said it should be, to be several feet above the line joining the tops of the two outer masts, then Mr. Hampden was to lose the five hundred pounds he had so rashly ventured. Everything was conducted in accordance with the arrangements agreed upon. The editor of a wellknown sporting paper acted as stakeholder, and unprejudiced umpires were to decide as to what actually was seen through the telescope. It need scarcely be said that the accepted theory held its own, and that Mr. Hampden lost his money. He scarcely bore the loss with so good a grace as was to have been expected from a philosopher merely desirous of ascertaining the truth. His wrath was not expended on Parallax, whom he might have suspected of having led him astray; nor does he seem to have been angry with himself, as would have seemed natural. All his anger was reserved for those who still continued to

believe in the earth's rotundity. Whether he believed that the Bedford water had risen under the middle boat to oblige Mr. Wallace, or how it came to pass that his own chosen experiment had failed him, does not appear.

The subsequent history of this matter has been unpleasant. It illustrates, unfortunately but too well, the mischief which may ensue from the tricks of those who make a trade of paradox-tricks which would be scarce possible, however, if text-books of science were more carefully written and by those only who are really acquainted with the subject of which they treat.

The book which originally led to Mr. Hampden's misfortunes, and has misled not a few, ought to have deceived none. I have already mentioned the statement on which Parallax (whose true name is Rowbotham) rested his theory. Of course, if that statement had been true-if he had, with his eye a few inches from the surface of the water of the Bedford Canal, seen an object close to the surface six miles from him-there manifestly would have been something wrong in the accepted theory about the earth's rotundity. So, also, if a writer were to announce a new theory of gravity, stating as the basis of his theory that a heavy missile which he had thrown into the air had gone upwards on a serpentine course to the moon, any one who accepted the statement would be logically bound to admit at least that the fact described was inconsistent with the accepted theory. But no one would accept such a statement; and no one should have accepted Mr. Rowbotham's statement.

His statement was believed, however, and perhaps is still believed by many. Twenty years ago, De Morgan wrote that the founder of the zetetic astronomy gained great praise from provincial newspapers for his ingenuity in proving that the earth is a flat, surrounded by ice,' with the north polar ice in the middle. Some of the journals rather incline to this view: but the "Leicester Advertiser" thinks that the statement "would seem to invalidate some of the most important conclusions of modern astronomy;" while the "Norfolk Herald" is clear that "there must be great error on one side or the other." The fact is worth noting that from 1849

to 1857 arguments on the roundness or flatness of the earth did itinerate. I have no doubt they did much good, for very few persons have any distinct idea of the evidence for the rotundity of the earth. The "Blackburn Standard" and "Preston Guardian" (December 12 and 16, 1849), unite in stating that the lecturer ran away from his second lecture at Burnley, having been rather too hard pressed, at the end of his first lecture, to explain why the large hull of a ship disappeared before the masts. The persons present and waiting for the second lecture assuaged their disappointment by concluding that the lecturer had slipped off the ice edge of his flat disc, and that he would not be seen again till he peeped up on the opposite side.' . . . The zetetic system,' proceeds De Morgan, 'still lives in lectures and books; as it ought to do, for there is no way of teaching a truth comparable to opposition. The last I heard of it was in lectures at Plymouth, in October 1864. Since this time a prospectus has been issued of a work entitled "The Earth not a Globe;" but whether it has been published I do not know.'

The book was published soon after the above was written, and De Morgan gives the following quaint account of it August 28, 1865. The zetetic astronomy has come into my hands. When in 1851 I went to see the Great Exhibition I heard an organ played by a performer who seemed very desirous to exhibit one particular stop. "What do you think of that stop?" I was asked. That depends on the name of it," said I. "Oh! what can the name of it have to do with the sound?that which we call a rose,' &c." "The name has everything to do with it if it be a flute stop, I think it very harsh; but if it be a railway-whistle stop, I think it very sweet." So as to this book if it be childish, it is clever; if it be mannish, it is unusually foolish. The flat earth floating tremulously on the sea; the sun moving always over the flat, giving day when near enough, and night when too far off; the self-luminous moon, with a semi-transparent invisible moon created to give her an eclipse now and then; the new law of perspective, by which the vanishing of the hull before the masts, usually thought to prove the earth globular, really proves

it flat; all these and other things are well fitted to form exercises for a person who is learning the elements of astronomy. The manner in which the sun dips into the sea, especially in tropical climates, upsets the whole. Mungo Park, I think, gives an African hypothesis which explains phenomena better than this. The sun dips into the Western ocean, and the people there cut him in pieces, fry him in a pan, and then join him together again; take him round the under way, and set him up in the East. I hope this book will be read, and that many will be puzzled by it; for there are many whose notions of astronomy deserve no better fate. There is no subject on which there is so little accurate conception as on that of the motions of the heavenly bodies.* The author, though confident in the extreme, neither impeaches the honesty of those whose opinion he assails, nor allots them any future inconvenience: in these points he is worthy to live on a globe and to rotate in twenty-four hours.'

I chanced to reside near Plymouth when Mr. Rowbotham lectured there in October 1864. It will readily be understood that, in a town where there are so many naval men, his lectures were not altogether so successful as they have sometimes been in small inland towns. Numbers of naval officers, however, who were thoroughly well assured of the fact that the earth is a globe, were not able to demolish the crafty arguments of Parallax publicly, during the discussions which he challenged at the close of each lecture. He was too skilled in that sort of evasion which his assumed name (as

* The Astronomer Royal once told me that he had found that few persons have a clear conception of the fact that the stars rise and set. Still fewer know how the stars move, above the horizon, which move on large circles, which stars rise and set, which are always which on small ones; though a few hours' observation on half-a-dozen nights in a year (such observations being continuous, but made only at hourly intervals) would show It is odd to find clearly how the stars move. even some who write about astronomy mak ing mistakes on matters so elementary. For instance, in a primer of astronomy recently published, it is stated that the stars which pass overhead in London rise and set on a slant-the real fact being that those stars never rise or set at all, never coming within some two dozen moon-breadths of the horizon.

interpreted by Liddell and Scott) suggests, to be readily cornered. When an argument was used which he could not easily meet, or seem to meet, he would say simply: 'Well, sir, you have now had your fair share of the discussion; let some one else have his turn.' It was stated in the newspapers that one of his audience was so wrathful with the lecturer on account of these evasions, that he endeavored to strike Parallax with a knobbed stick at the close of the second lecture; but probably there was no real foundation for the story.

Mr. Rowbotham did a very bold thing, however, at Plymouth. He undertook to prove, by observations made with a telescope upon the Eddystone Lighthouse from the Hoe and from the beach, that the surface of the water is flat. From the beach, usually only the lantern can be seen. From the Hoe, the whole of the lighthouse is visible under favor able conditions. Duly on the morning appointed, Mr. Rowbotham appeared. From the Hoe a telescope was directed towards the lighthouse, which was well seen, the morning being calm and still, and tolerably clear. On descending to the beach it was found that, instead of the whole lantern being visible as usual, only half could be seen-a circumstance doubtless due to the fact that the air's refractive power, which usually diminishes the dip due to the earth's curvature by about one-sixth part, was less efficient that morning than usual. The effect of the peculiarity was manifestly unfavorable to Mr. Rowbotham's theory. The curvature of the earth produced a greater difference than usual between the appearance of a distant object as seen from a certain high station and from a certain low station (though still the difference fell short of that which would be shown if there were no air). But Parallax claimed the peculiarity observable that morning as an argument in favor of his flat earth. It is manifest, he said, that there is something wrong about the accepted theory; for it tells us that so much less of the lighthouse should be seen from the beach than from the Hoe, whereas less still was seen. And many of the Plymouth folk went away from the Hoe that morning, and from the second lecture in which Parallax triumphantly quoted the results of the ob

servation, with the feeling, which had been expressed seven years before in the 'Leicester Advertiser,' that 'some of the most important conclusions of modern astronomy had been seriously invalidated.' If our books of astronomy, in referring to the effects of the earth's curvature, had only been careful to point out how surveyors and sailors and those who build lighthouses take into account the modifying effects of atmospheric refraction, and how these effects have long been known to vary with the temperature and pressure of the air, this mischief would have been avoided. It would not be fair to say of the persons misled on that occasion by Parallax that they deserved no better; since the fault is not theirs as readers, but that of careless or ill-informed writers.

Another experiment conducted by Parallax the same morning was creditable to his ingenuity. Nothing better, perhaps, was ever devised to deceive people, apparently by ocular evidence, into the belief that the earth is flat-nor is there any clearer evidence of the largeness of the earth's globe compared with our ordinary measures. On the Hoe, some ninety or a hundred feet above the sea-level, he had a mirror suspended in a vertical position facing the sea, and invited the bystanders to look in that mirror at the sea-horizon. To all appearance the line of the horizon corresponded exactly with the level of the eye-pupils of the observer. Now, of course, when we look into a mirror whose surface is exactly vertical, the line of sight to the eye-pupils of our image in the mirror is exactly horizontal; whereas the line of sight from the eyes to the image of the sea-horizon is depressed exactly as much as the line from the eyes to the real sea-horizon. Here, then, seemed to be proof positive that there is no depression of the sea-horizon; for the horizontal line to the image of the eye-pupil seemed to coincide exactly with the line to the image of the seahorizon. It is not necessary to suppose here that the mirror was wrongly adjusted, though the slightest error of adjustment would affect the result either favorably or unfavorably for Parallax's flatearth theory. It is a matter of fact that, if the mirror were perfectly vertical, only very acute vision could detect the depres

sion of the image of the sea-horizon below the image of the eye-pupil. The The depression can easily be calculated for any given circumstances. Parallax encouraged observers to note very closely the position of the eye-pupil in the image, so that most of them approached the image within about ten inches, or, the glass within about five. Now, in such a case, for a height of one hundred feet above the sea-level the image of the seahorizon would be depressed below the image of the eye-pupil, less than threehundredths of an inch-an amount which could not be detected by one eye in a hundred. The average diameter of the pupil itself is one-fifth of an inch, or about seven times as great as the depression of the sea-horizon in the case supposed. It would require very close observation and a good eye to determine whether a horizontal line seen on either side of the head were on the level of the centres of the eye-pupils, or lower by about one-seventh of the breadth of either pupil.

The experiment is a pretty one, however, and well worth trying by anyone who lives near to the sea-shore and seacliffs. But there is a much more effective experiment which can be much more easily tried-only it is open to the disadvantage that it at once demolishes the argument of our friend Parallax. It occurred to me while I was writing the above paragraph. Let a very small mirror (it need not be larger than a sixpence) be so suspended to a small support and so weighted that when left to itself it hangs with its face perfectly vertical-an arrangement which any competent optician will easily secure-and let a fine horizontal line or several horizontal lines be marked on the mirror; which, by the way, should be a metallic one, as its indications will then be aitogether more trustworthy. This mirror can be put into the waistcoat pocket and conveniently carried to much greater heights than the mirror used by Parallax. Now, at some considerable height -say five or six hundred feet above the sea-level, but a hundred or even fifty will suffice-look into this small mirror while facing the sea. The true horizon will then be seen to be visibly below the centre of the eye-pupil-visibly in this case because the horizontal line traced

on the mirror can be made to coincide with the sea-horizon exactly, and will then be found not to coincide with the centre of the eye-pupil. Such an instrument could be readily made to show the distance of the sea-horizon, which at once determines the height of the observer above the sea-level. For this purpose all that would be necessary would be a means of placing the eye at some definite distance from the small mirror, and a fine vertical scale on the mirror to show the exact depression of the sea-horizon. For balloonists such an instrument would sometimes be useful, as showing the elevation independently of the barometer, whenever any portion of sea-horizon was in view.

The mention of balloon experiences leads me to another delusive argument of the earth-flatteners.* It has been the experience of all aeronauts that, as the balloon rises, the appearance of the earth is by no means what would be expected from the familiar teachings in our books of astronomy. There is a picture in most of these books representing the effect of ascent above the sea-level in depressing the line of sight to the horizon, and bringing more and more into view the convexity of the earth's globe. One would suppose, from the picture, that when an observer is at a great height the earth would appear to rise under him, like some great round and well-curved shield whose convexity was towards him. Instead of this, the aeronaut finds the earth presenting the appearance of a great hollow basin, or of the concave side of a well-curved shield. The horizon seems to rise as he rises, while the earth beneath him sinks lower and lower. A somewhat similar phenomenon may be noted when, after ascending the landward side of a high cliff, we come suddenly upon a view of the seainvariably the sea-horizon is higher than we expected to find it. Only, in this case, the surface of the sea seems to rise

In passing, let me note that, of course, I am not discussing the arguments of paradoxists with the remotest idea of disproving them. They are not, in reality, worth the trouble. But they show where the general reader of astronomical text-books, and other such works, is likely to go astray, and thus conveniently indicate matters whose explanation may be useful or interesting.

from the beach below towards the distant horizon convexly not concavely; the reason of which I take to be this, that the waves, and especially long rollers or uniform large ripples, teach the eye to form true conceptions of the shape of the sea-surface even when the eye is deceived as to the position of the sea-horizon. Indeed, I should much like to know what would be the appearance of the sea from a balloon, when no land was in sight (though I do not particularly wish to make the observation myself): the convexity discernible, for the reason just named, would contend strangely with the concavity imagined, for the reason now to be indicated.

The deception arises from the circumstance that the scene displayed below and around the balloon is judged by the eye from the experience of more familiar scenes. The horizon is depressed, but so little that the eye cannot detect the depression, especially where the boundary of the horizon is irregular. It is here that the text-book pictures mislead; for they show the depression as far too great to be overlooked, setting the observer sometimes about two thousand miles above the sea-level. The eye, then, judges the horizon to be where it usually is on the same level as the observer; but looking downwards, the eye perceives, and at once appreciates if it does not even exaggerate, the great depth at which the earth lies below the balloon. The appearance, then, as judged by the eye, is that of a mighty basin whose edge rises up all round to the level of the balloon, while its bottom lies two or three miles or more below the balloon.

A

The zetetic faithful reason about this matter as though the impressions of the senses were trustworthy under all conditions, familiar or otherwise; whereas, in point of fact, we know that the senses often deceive, even under familiar conditions, and almost always deceive under conditions which are not familiar. person, for example, accustomed to the mist and haze of our British air, is told by the sense of sight, when he is travelling where a clearer atmosphere prevails, that a mountain forty miles from him is a hill a few miles away. On the other hand, an Italian travelling through the Highlands is impressed with the belief that all the features of the scenery

are much larger (because he supposes them much more remote) than they really are. A hundred such instances of deception might easily be cited. The conditions under which the aeronaut observes the earth are certainly less familiar than those under which the Briton views the Alps and Apennines, or the Italian views Ben Lomond or Ben Lawers. It would be rash, therefore, even if no other evidence were available, to reject the faith that the earth is a globe because, as seen from a balloon, it looks like a basin. Indeed, to be strictly logical, the followers of Parallax ought on this account to adopt the faith that the earth is not flat, but basin-shaped; which hitherto they have not been ready to do.

We have seen that Parallax describes a certain experiment on the Bedford Level, which, if made as he states, would have shown certainly that something was wrong in the accepted system-for a sixmile straight-edge along water would be as severe a blow to the belief in a round earth, as a straight line on the sea-surface from Queenstown to New York. Another curious experiment adorns his little book, which, if it could be repeated successfully before a dozen trustworthy witnesses, would rather astonish men of science. Having, he says, by certain reasoning-altogether erroneous, but that is a detail-convinced himself that, on the accepted theory, a bullet fired vertically upwards ought to fall far to the west of the place whence it was fired, he carefully fixed an air-gun in a vertical position, and fired forty bullets vertically upwards. All these fell close to the gun -which is not surprising, though it must have made such an experiment rather dangerous; but two fell back into the barrel itself-which certainly was very surprising indeed. One might fairly challenge the most experienced gunner in the world to achieve one such vertical shot in a thousand trials; two in forty. bordered on the miraculous.

The earth-flatteners I have been speak、 ing of claim, as one of their objects, the defence of Scripture. But some of the earth-flatteners of the last generation (or a little further back) took quite another view of the matter. For instance, Sir Richard Phillips, a more vehement earthflattener than Parallax, was so little interested in defending the Scriptures, that