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Zetetic Astronomy, by 'Parallax' (pseud. Samuel Birley Rowbotham), [1881], at sacred-texts.com
IF a ball is allowed to drop from the mast-head of a ship at rest, it will strike the deck at the foot of the mast. If the same experiment is tried with a ship in motion, the same result will follow; because, in the latter case, the ball is acted upon simultaneously by two forces at right angles to each other--one, the momentum given to it by the moving ship in the direction of its own motion; and the other, the force of gravity, the direction of which is at right angles to that of the momentum. The ball being acted upon by the two forces together, will not go in the direction of either, but will take a diagonal course, as shown in the following diagram, fig. 46.
The ball passing from A to C, by the force of gravity, and having, at the moment of its liberation, received a momentum . from the moving ship in the direction A, B, will, by the conjoint action of the two forces A, B, and A, C, take the direction A, D, falling at D, just as it would have fallen at C, had the vessel remained at rest.
It is argued by those who hold that the earth is a revolving globe, that if a ball is dropped from the mouth of a deep mine, it reaches the bottom in an apparently vertical direction, the same as it would if the earth were motionless. In the same way, and from the same cause, it is said that a ball allowed to drop from the top of a tower, will fall at the base. Admitting the fact that a ball dropped down a mine, or let fall from a high tower, reaches the bottom in a direction parallel to the side of either, it does not follow therefrom that the earth moves. It only follows that the earth might move, and yet allow of such a result. It is certain that such a result would occur on a stationary earth; and it is mathematically demonstrable that it would also occur on a revolving earth; but the question of motion or non-motion--of which is the fact it does not decide. It gives no proof that the ball falls in a vertical or in a diagonal direction. Hence, it is logically valueless. We must begin the enquiry with an experiment which does not involve a supposition or an ambiguity, but which will decide whether motion does actually or actually does not exist. It is certain, then, that the path of a ball, dropped from the mast-head of a stationary ship will be vertical. It is also certain that, dropped down a deep mine, or from the top of a high
tower, upon a stationary earth, it would be vertical. It is equally certain that, dropped from the mast-head of a moving ship, it would be diagonal; so also upon a moving earth it would be diagonal. And as a matter of necessity, that which follows in one case would follow in every other case, if, in each, the conditions were the same. Now let the experiment shown in fig. 46 be modified in the following way:--
Let the ball be thrown upwards from the mast-head of a stationary ship, and it will fall back to the mast-head, and pass downwards to the foot of the mast. The same result would follow if the ball were thrown upwards from the mouth of a mine, or the top of a tower, on a stationary earth. Now put the ship in motion, and let the ball be thrown upwards. It will, as in the first instance, partake of the two motions--the upward or vertical, A, C, and the horizontal, A, B, as shown in fig. 47; but
because the two motions act conjointly, the ball will take the diagonal direction, A, D. By the time the ball has arrived at
[paragraph continues] D, the ship will have reached the position, 13; and now, as the two forces will have been expended, the ball will begin to fall, by the force of gravity alone, in the vertical direction, D, B, H; but during its fall towards H, the ship will have passed on to the position S, leaving the ball at H, a given distance behind it.
The same result will be observed on throwing a ball upwards from a railway carriage, when in rapid motion, as shown in the following diagram, fig. 48. While the carriage or tender passes
from A to B, the ball thrown upwards, from A towards (2, will reach the position D; but during the time of its fall from D to B, the carriage will have advanced to S, leaving the ball behind at B, as in the case of the ship in the last experiment.
The same phenomenon would be observed in a circus, during the performance of a juggler on horseback, were it not that the balls employed are thrown more or less forward, according to the rapidity of the horse's motion. The juggler standing in the ring, on the solid ground, throws his balls as vertically as he can, and they return to his hand; but when on the back of a rapidly-moving horse, he should throw the balls vertically, before they fell
back to his hands, the horse would have taken him in advance, and the whole would drop to the ground behind him. It is the same in leaping from the back of a horse in motion. The performer must throw himself to a certain degree forward. If he jumps directly upwards, the horse will go from under him, and he would fall behind.
Thus it is demonstrable that, in all cases where a ball is thrown upwards from an object moving at right angles to its path, that ball will come down to a place behind the point from which it was thrown; and the distance at which it falls behind depends upon the time the ball has been in the air. As this is the result in every instance where the experiment is carefully and specially performed, the same would follow if a ball were discharged from any point upon a revolving earth. The causes or conditions operating being the same, the same effect would necessarily follow.
The experiment shown in fig. 49, demonstrates, however, that
these causes, or conditions, or motion in the earth, do not exist.
[paragraph continues] A strong cast-iron cannon was placed with the muzzle upwards. The barrel was carefully tested with a plumb line, so that its true vertical direction was secured; and the breech of the gun was firmly embedded in sand up to the touch-hole, against which a piece of slow match was placed. The cannon had been loaded with powder and ball, previous to its position being secured. At a given moment the slow match at D was fired, and the operator retired to a shed. The explosion took place, and the ball was discharged in the direction A, B. In thirty seconds the ball fell back to the earth, from B to C; the point of contact, C, was only 8 inches from the gun, A. This experiment has been many times tried, and several times the ball fell back upon the mouth of the cannon; but the greatest deviation was less than 2 feet, and the average time of absence was 28 seconds; from which it is concluded that the earth on which the gun was placed did not move from its position during the 28 seconds the ball was in the atmosphere. Had there been motion in the direction from west to east, and at the rate of 600 miles per hour (the supposed velocity in the latitude of England), the result would have been as shown in fig. 49. The ball, thrown by the powder in the direction A, C, and acted on at the same moment by the earth's motion in the direction A, B, would take the direction A, D; meanwhile the earth and the cannon would have reached the position B, opposite to D. On the ball beginning to descend, and during the time of its descent, the gun would have passed on to the position S, and the ball would have dropped at B, a consider-able distance behind the point S. As the average time of the ball's absence in the atmosphere was 28 seconds--14 going upwards, and 14 in falling--we have only to multiply the time by the supposed velocity of the earth, and we find that instead of the ball coming down to within a few inches of the
muzzle of the gun, it should have fallen behind it a distance of 8400 feet, or more than a mile and a half! Such a result is utterly destructive of the idea of the earth's possible rotation.
The reader is advised not to deceive himself by imagining that the ball would take a parabolic course, like the balls and shells from cannon during a siege or battle. The parabolic curve could only be taken by a ball fired from a cannon inclined more or less from the vertical; when, of course, gravity acting in an angular direction against the force of the gunpowder, the ball would be forced to describe a parabola. But in the experiment just detailed, the gun was fixed in a perfectly vertical direction, so that the ball would be fired in a line the very contrary to the direction of gravity. The force of the powder would drive it directly upwards, and the force of gravity would pull it directly downwards. Hence it could only go up in a right line, and down or back to its starting point; it could not possibly take a path having the slightest degree of curvature. It is therefore demanded that, if the earth has a motion from west to east, a ball, instead of being dropped down a mine, or allowed to fall from the top of a tower, shall be shot upwards into the air, and from the moment of its beginning to descend, the surface of the earth shall turn from under its direction, and it would fall behind, or to the west of its line of descent. On making the most exact experiments, however, no such effect is observed; and, therefore, the conclusion is in every sense unavoidable, that THE EARTH HAS NO MOTION OF ROTATION.
When sitting in a rapidly-moving railway carriage, let a spring-gun 1 be fired forward, or in the direction in which the train is moving. Again, let the same gun be fired, but in the opposite direction; and it will be found that the ball or other projectile will always go farther in the first case than in the latter.
If a person leaps backwards from a horse in full gallop, he cannot jump so great a distance as he can by jumping forward. Leaping from a moving sledge, coach, or other object, backwards or forwards, the same results are experienced.
Many other practical cases could be cited to show that any body projected from another body in motion, does not exhibit the same behaviour as it does when projected from a body at rest. Nor are the results the same when projected in the same direction as that in which the body moves, as when projected in the opposite direction; because, in the former case, the projected body receives its momentum from the projectile force, plus that given to it by the moving body; and in the latter case, this momentum, minus that of the moving body. Hence it would be found that if the earth is a globe, and moving rapidly from west to east, a cannon fired in a due easterly direction would send a ball to a greater distance than it would if fired in a due westerly direction. But the most experienced artillerymen--many of whom have had great practice, both at home and abroad, in almost every latitude--have declared that no difference whatever is
observable. That in charging and pointing their guns, no, difference in the working is ever required, notwithstanding that the firing is at every point of the compass. Gunners in war ships have noticed a considerable difference in the results of their firing from guns at the bow, when sailing rapidly towards the object fired at, and when firing from guns placed at the stern while sailing away from the object: and in both cases the results are different to those observed when firing from a ship at perfect rest. These details of practical experience are utterly incompatible with the supposition of a revolving earth.
During the period of the Crimean War, the subject of gunnery, in connection with the earth's rotation, was one which occupied the attention of many philosophers, as well as artillery officers and statesmen. About this time, Lord Palmerston, as Prime Minister, wrote the following letter to Lord Panmure, the Secretary for War:--
"December 20th, 1857.
"My dear Panmure.
"There is an investigation which it would be important and at the same time easy to make, and that is, whether the rotation of the earth on its axis has any effect on the curve of a cannon-ball in its flight. One should suppose that it has, and that while the cannon-ball is flying in the air, impelled by the gunpowder in a straight line from the cannon's mouth, the ball would not follow the rotation of the earth in the same manner which it would do if lying at rest on the earth's surface. If this be so, a ball fired in the meridional direction--that is to say, due south or due north--ought to deviate to the west of the object at which it was.
aimed, because during the time of flight, that object will have gone to the east somewhat faster than the cannon-ball will have done. In like manner, a ball fired due east, ought to fly less far upon the earth's surface than a ball fired due west, the charges being equal, the elevation the same, and the atmosphere perfectly still. It must be remembered, however, that the ball, even after it has left the cannon's mouth, will retain the motion from west to east which it had before received by the rotation of the earth on whose surface it was; and it is possible, therefore, that, except at very long ranges, the deviations above mentioned may in practice turn out to be very small, and not deserving the attention of an artilleryman. The trial might be easily made in any place in which a free circle of a mile or more radius could be obtained; and a cannon placed in the centre of that circle, and fired alternately north, south, east, and west, with equal charges, would afford the means of ascertaining whether each shot flew the same distance or not.
"Yours sincerely,
"PALMERSTON."
The above letter was published, by Lord Dalhousie's permission, in the "Proceedings of the Royal Artillery Institution for 1867."
It will be observed that Lord Palmerston thought that firing eastwards, or in the direction of the earth's supposed rotation, the ball would "fly less far upon the earth's surface than a ball fired due west." It is evident that his Lordship did not allow for the extra impulse given to the ball by the earth's motion. But the answer given by the advocates of the theory of the earth's motion is the following: Admitting that a ball fired from the
earth at rest would go, say two miles, the same ball, fired from the earth in motion, would go, say three miles; but during the time the ball is passing through the air, the earth will advance one mile in the same direction. This one mile deducted from the three miles which the ball actually passes through the air, leaves the two miles which the ball has passed in advance of the cannon; so that practically the distance to which a ball is projected is precisely the same upon a moving earth as it is upon the earth at rest. The following diagram, fig. 50, will illustrate the path of a ball under the conditions above described.
Let the curved line A, B, represent the distance a ball would fly from a cannon placed at A, upon the earth, at rest. Let A, C, represent the distance the same ball would fly from the conjoint action of the powder in the cannon, A, and the earth's rotation in the direction A, C. During the time the ball would require to traverse the line A, C, the earth and the cannon would arrive at the point D; hence the distance D, C, would be the same as the distance A, B.
The above explanation is very ingenious, and would be perfectly satisfactory if other considerations were not involved in it. For instance, the above explanation does not prove the earth's motion--it merely supposes it; but
as in all other cases where the result of supposition is explained, it creates a dilemma. It demands that during the time the ball is in the air, the cannon is advancing in the direction of the supposed motion of the earth. But -this is granting the conditions required in the experiments represented by figs. 47, 48, and 49. If the cannon can advance in the one case, it must in the other; and as the result in the experiment represented at fig. 49, was that the ball, when fired vertically, essentially returned to the vertical cannon; that cannon could not have advanced, and therefore the earth could not have moved.
Take a large grinding stone, and let the whole surface of the rim be well rubbed over with a saturated solution of phosphorus in olive oil; or cover the stone with several folds of coarse woollen cloth or flannel, which saturate with boiling water. If it be now turned rapidly round, by means of a multiplying wheel, the phosphoric vapour, or the steam from the flannel, which surrounds it and which may be called its atmosphere--analogous to the atmosphere of the earth--will be seen to follow the direction of the revolving surface. Now the surface of the earth is very irregular in its outline, mountains rising several miles above the sea, and ranging for hundreds of miles in every possible direction; rocks, capes, cliffs, gorges, defiles, caverns, immense forests, and every other form of ruggedness and irregularity calculated to adhere to and drag along whatever medium may exist upon it: and if it is a globe revolving on its axis, with
the immense velocity at the equator of more than a thousand miles an hour, it is exceedingly difficult if not altogether impossible to conceive of such a mass moving at such a rate, and yet not taking the atmosphere along with it. When it is considered, too, that the medium which it is said surrounds the earth and all the heavenly bodies, and filling all the vast spaces between them, is almost too ethereal and subtle to offer any sensible resistance, it is still more difficult to understand how the atmosphere can be prevented being carried forward with the earth's rapidly revolving surface. Study the details of pneumatics or hydraulics as we may, we cannot suggest an experiment which will show the possibility of such a thing. Hence we are compelled to conclude that if the earth revolves, the atmosphere revolves also, and in the same direction. If the atmosphere rushes forward from west to east continually, we are again obliged to conclude that whatever floats or is suspended in it, at any altitude, must of necessity partake of its eastward motion. A piece of cork, or any other body floating in still water, will be motionless, but let the water be put in motion, in any direction whatever, and the floating bodies will move with it, in the same direction and with the same velocity. Let the experiment be tried in every possible way, and these results will invariable follow. Hence if the earth's atmosphere is in constant motion from west to east, all the different strata which are known to exist in it, and all the various kinds of clouds and vapours which float in it must of mechanical necessity move rapidly eastwards. But what is the fact? If we fix upon any star as a standard or datum outside the visible atmosphere, we may sometimes observe a stratum of clouds going for hours together in a direction the very opposite to that in which the earth is supposed to be moving. See fig. 51, which represents a section of a
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Fig. 51.
globe, surrounded with an atmosphere, moving at the rate of 1042 miles an hour at the equator, and in the direction of the arrows 1, 2, 3, while a stream of clouds are moving in the opposite direction, as indicated by the arrows, 4, 5, 6. Not only may a stratum of clouds be seen moving rapidly from east to west, but at the same moment other strata may often be seen moving from north to south, and from south to north. It is a fact well known to aeronauts, that several strata of atmospheric air are often moving in as many different directions at the same time. It is a knowledge of this fact which leads an experienced aeronaut, when desiring to rise in a balloon, and to go in a certain direction, not to regard the manner in which the wind is blowing on the immediate surface of the earth, because he knows that at a greater altitude, it may be going at right angles, or even in opposite and in various ways simultaneously. To ascertain whether and at what altitude a current is blowing in the desired direction, small, and so-called "pilot-balloons" are often sent up and carefully observed in their ascent. If during the passage of one of these through the variously moving
strata, it is seen to enter a current which is going in the direction desired by the aëronaut, the large balloon is then ballasted in such a manner that it may ascend at once to the altitude of such current, and thus to proceed on its journey.
On almost any moonlight and cloudy night, different strata may be seen not only moving in different directions but, at the same time, moving with different velocities; some floating past the face of the moon rapidly and uniformly, and others passing gently along, sometimes becoming stationary, then starting fitfully into motion, and often standing still for minutes together. Some of those who have ascended in balloons for scientific purposes have recorded that as they have rapidly passed through the atmosphere, they have gone though strata differing in temperature, in density, and in hygrometric, magnetic, electric, and other conditions. These changes have been noticed both in ascending and descending, and in going for miles together at the same altitude.
"On the 27th November, 1839, the sky being very clear, the planet Venus was seen near the zenith, notwithstanding the brightness of the meridian sun. It enabled us to observe the higher stratum of clouds to be moving in an exactly opposite direction to that of the wind--a circumstance which is frequently recorded in our meteorological journal both in the north-east and south-east trades, and has also often been observed by former voyagers. Captain Basil Hall witnessed it from the summit of the Peak of Teneriffe; and Count Strzelechi, on ascending the volcanic mountain of Kiranea, in Owhyhee, reached at 4000 feet an elevation above that of the trade wind, and experienced the influence of an opposite current of air of a
different hygrometric and thermometric condition. . . . Count Strzelechi further informed me of the following seemingly anomalous circumstance--that at the height of 6000 feet he found the current of air blowing at right angles to both the lower strata, also of a different hygrometric and thermometric condition, but warmer than the inter-stratum." 1
Such a state of the atmosphere is compatible only with the fact which other evidence has demonstrated, that the earth is at rest. Were it otherwise-if a spherical mass of eight thousand miles in diameter, with an atmosphere of only fifty miles in depth, or relatively only as a sheet of note paper pasted upon a globe of one yard in diameter, and lying upon a rugged, adhesive, rapidly revolving surface, there is nothing to prevent such an atmosphere becoming a mingled homogeneous mass of vapour.
Notwithstanding that all practical experience, and all specially instituted experiments are against the possibility of a moving earth, and an independent moving and non-moving atmosphere, many mathematicians have endeavoured to "demonstrate" that with regard to this earth, such was actually the case. The celebrated philosophic divine, Bishop Wilkins, was reasoned by the theorists of his day into this belief; and, in consequence, very naturally suggested a new and easy way of travelling. He proposed that large balloons should be provided with apparatus to work against the varying currents of the air. On ascending to a proper altitude, the balloon was to be kept practically in a state of rest, while the earth revolved underneath it; and when the desired locality came into view, to stop the working of
the fans, &c., to let out the gas, and drop down at once to the earth's surface. In this simple way New York would be reached in a few hours, or rather New York would reach the balloon, at the rate, in the latitude of England, of more than 600 miles an hour.
The argument involved in the preceding remarks against the earth's rotation has often been met by the following, at first sight, plausible statement. A ship with a number of passengers going rapidly in one continued direction, like the earth's atmosphere, could nevertheless have upon its deck a number of distinctly and variously moving objects, like the clouds in the atmosphere. The clouds in the atmosphere are compared to the passengers on the deck of a ship; so far the cases are sufficiently parallel, but the passengers are sentient beings, having within themselves the power of distinct and independent motions: the clouds are the reverse; and here the parallelism fails. One case is not illustrative of the other, and the supposition of rotation in the earth remains without a single fact or argument in its favour. Birds in the air, or fish and reptiles in the water, would have offered a parallel and illustrative case, but these, like the passengers on the ship's deck, are sentient and independent beings; clouds and vapours are dependent and non-sentient, and must therefore of necessity move with, and in the direction of, the medium in which they float.
Everything actually observable in Nature; every argument furnished by experiment; every legitimate process of reasoning; and, as it would seem, everything which it is possible for the human mind practically to conceive, combine
in evidence against the doctrine of the earth's motion upon axes.
ORBITAL MOTION.--The preceding experiments and remarks, logically and mathematically suffice as evidence against the assumed motion of the earth in an orbit round the sun. It is difficult, if not impossible, to understand how the behaviour of the ball thrown from a vertical gun should be other in relation to the earth's forward motion in space, than it is in regard to its motion upon axes. Besides, it is demonstrable that it does not move upon axes, and therefore, the assumption that it moves in an orbit, is utterly useless for theoretical purposes. The explanation of phenomena, for which the theory of orbital and diurnal motion was framed, is no longer possible with a globular world rushing through space in a vast elliptical orbit, but without diurnal rotation. Hence the earth's supposed orbital motion is logically void, and non-available, and there is really no necessity for either formally denying it, or in any way giving it further consideration. But that no point may be taken without direct and practical evidence, let the following experiment be tried.
Take two carefully-bored metallic tubes, not less than six feet in length, and place them one yard asunder, on the opposite sides of a wooden frame, or a solid block of wood or stone: so adjust them that their centres or axes of vision shall be perfectly parallel to each other. The following diagram will show the arrangement.
Now, direct them to the plane of some notable fixed star, a few seconds previous to its meridian time. Let an observer be stationed at each tube, as at A, B; and the moment the star appears in the tube A, T, let a loud knock or other signal be given, to be repeated by the observer at the tube B, T, when he first sees the same star. A distinct period of time will elapse between the signals given. The signals will follow each other in very rapid succession, but still, the time between is sufficient to show that the same star, S, is not visible at the same moment by two parallel lines of sight A, S, and B, C, when only one yard asunder. A slight inclination of the tube, B, C, towards the first tube A, S, would be required for the star, S, to be seen through both tubes at the same instant. Let the tubes remain in their position for six months; at the end of which time the same observation or experiment will produce the same results--the star, S, will be visible at the same meridian time, without the slightest alteration being required in the direction of the tubes: from which it is concluded that if the earth had moved one single yard in an orbit through space, there would at least be observed the slight inclination of the tube, B, C, which the difference in position of one yard had previously required.
[paragraph continues] But as no such difference in the direction of the tube B, C, is required, the conclusion is unavoidable, that in six months a given meridian upon the earth's surface does not move a single yard, and therefore, that the earth has not the slightest degree of orbital motion.
Copernicus required, in his theory of terrestrial motions, that the earth moved in an extensive elliptical path round the sun, as represented in the following diagram, fig 53, where S is the
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Fig. 53.
sun, A, the earth in its place in June, and B, its position in December; when desired to offer some proof of this orbital motion he suggested that a given star should be selected for observation on a given date; and in six months afterwards a second observation of the same star should be made. The first observation A, D, fig. 53, was recorded; and on observing again at the end of six months, when the earth was supposed to have passed to B, the other side of its orbit, to the astonishment of the assembled astronomers, the star was observed in exactly the
same position, B, C, as it had been six months previously! It was expected that it would be seen in the direction B, D, and that this difference in the direction of observation would demonstrate the earth's motion from A to B, and also furnish, with the distance A, S, B, the elements necessary for calculating the actual distance of the star D.
The above experiment has many times been tried, and always with the same general result. No difference whatever has been observed in the direction of the lines of sight A, D, and B, C, whereas every known principle of optics and geometry would require, that if the earth had really moved from A to B, the fixed star D, should be seen in the direction B, D. The advocates of this hypothesis of orbital motion, instead of being satisfied, from the failure to detect a difference in the angle of observation, that the earth could not possibly have changed its position in the six months, were so regardless of all logical consistency, that instead of admitting, and accepting the consequences, they, or some of them, most unworthily declared that they could not yield up the theory, on account of its apparent value in explaining certain phenomena, but demanded that the star D, was so vastly distant, that, notwithstanding that the earth must have moved from A to B, this great change of position would not give a readable difference in the angle of observation at B, or in other words the amount of parallax (" annual parallax," it was called) was inappreciable!
Since the period of the above experiments, many have declared that a very small amount of "annual parallax" has been detected. But the proportion given by different observers has been so various, that nothing definite and satisfactory can yet be decided upon. Tycho Brahe, Kepler, and others, rejected the Copernican theory, principally
eon account of the failure to detect displacement or parallax of the fixed stars. Dr. Bradley declared that what many had called "parallax," was merely "aberration." But "Dr. Brinkley, in 1810, from his observations with a very fine circle in the Royal Observatory of Dublin, thought he had detected a parallax of 1″ in the bright star Lyra (corresponding to an annual displacement of 2″). This, however, proved to be illusory; and it was not till the year 1839, that Mr. Henderson, having returned from filling the situation of astronomer royal to the Cape of Good Hope, and discussing as series of observations made there with a large "mural circle," of the bright star, α Centauri, was enabled to announce as a positive fact the existence of a measurable parallax for that star, a result since fully confirmed with a very trifling correction by the observations of his successor, Sir T. Maclear. The parallax thus assigned α Centauri, is so very nearly a whole second in amount (0″.98), that we may speak of it as such. It corresponds to a distance from the sun of 18,918,000,000,000 British statute miles.
"Professor Bessel made the parallax of a star in the constellation Cygnus to be 0″.35. Later astronomers, going over the same ground, with more perfect instruments, and improved practice in this very delicate process 'of observation, have found a somewhat larger result, stated by one at 0″.57, and by another at 0″.51, so that we may take it at 0″.54, corresponding to somewhat less than twice the distance of a Centauri;" 1 or to nearly 38 billions of miles.
It might seem to a non-scientific mind that the differences
above referred to of only a few fractions of a second in the parallax of a star, constitute a very slight amount; but in reality such differences involve differences in the distance of such stars of millions of miles, as will be seen by the following quotation from the Edinburgh Review for June, 1850:--
"The rod used in measuring a base line is commonly ten feet long; and the astronomer may be said only to apply this very rod to measure the distance of the fixed stars! An error in, placing a fine dot, which fixes the length of the rod, amounting to one five-thousandth part of an inch, will amount to an excess, of 70 feet in the earth's diameter; of 316 miles in the sun's distance, and to 65,200,000 miles in that of the nearest fixed star!
"The second point to which we would advert is, that as the astronomer in his observatory has nothing to do with ascertaining length as distances, except by calculation, his whole skill and artifice are exhausted in the measurement of angles. For it is by these alone that spaces inaccessible can be compared. Happily a ray of light is straight. Were it not so (in celestial spaces at least) there were an end of our astronomy. It is as inflexible as adamant, which our instruments unfortunately are not. Now an angle of a second (3600 to a degree), is a subtle thing, it is an apparent breadth, utterly invisible to the unassisted eye, unless accompanied by so intense a splendour (as in the case of the fixed stars) as actually to raise by its effect on the nerve of sight a spurious image, having a sensible breadth. A silkworm's fibre subtends an angle of one second at 3½ feet distance. A ball 2½ inches in diameter must be removed in order to subtend an angle of one second, to 43,000 feet, or about 8 miles; while it would be utterly invisible to the sharpest sight aided even by a telescope of some power. Yet it is on the
measurement of one single second that the ascertainment of a sensible parallax in any fixed star depends; and an error of one-thousandth of that amount (a quantity still immeasurable by the most perfect of our instruments) would place a fixed star too far or too near by 200,000,000,000 of miles."
Sir John Herschel says:--
"The observations require to be made with the very best instruments, with the minutest attention to everything which can affect their precision, and with the most rigorous application of an innumerable host of 'corrections,' some large, some small, but of which the smallest, neglected or erroneously applied, would be quite sufficient to overlay and conceal from view the minute quantity we are in search of. To give some idea of the delicacies which have to be attended to in this inquiry, it will suffice to mention that the stability not only of the instruments used and the masonry which supports them, but of the very rock itself on which it is founded, is found to be subject to annual fluctuations capable of seriously affecting the result."
Dr. Lardner, in his "Museum of Science," page 179, makes use of the following words
"Nothing in the whole range of astronomical research has more baffled the efforts of observers than this question of the parallax. * * * Now, since, in the determination of the exact uranographical position of a star, there are a multitude of disturbing effects to be taken into account and eliminated, such as precession, nutation, aberration, refraction, and others, besides the proper motion of the star; and since, besides the errors of observation, the quantities of these are subject to more or less uncertainty, it will astonish no one to be told that they may en-tail upon the final result of the calculation, an error of 1″; and
if they do, it is vain to expect to discover such a residual phenomenon as parallax, the entire amount of which is less than one second."
The complication, uncertainty, and unsatisfactory state of the question of annual parallax, and therefore of the earth's motion in an orbit round the sun, as indicated by the several paragraphs above quoted, are at once and for ever annihilated by the simple fact, experimentally demonstrable, that upon a base line of only a single yard, there may be found a parallax, as certain and as great, if not greater, than that which astronomers pretend to find with the diameter of the earth's supposed orbit of many millions of miles as a base line. To place the whole matter, complicated, uncertain, and unsatisfactory as it is, in a concentrated form, it is only necessary to state as an absolute truth the result of actual experiment, that, a given fixed star will, when observed from the two ends of a base line of not more than three feet, give a parallax equal to that which it is said is observed only from the two extremities of the earth's orbit, a distance or base line, of one hundred and eighty millions of miles! So far, then, from the earth having passed in six months over the vast space of nearly two hundred millions of miles, the combined observations of all the astronomers of the whole civilized world have only resulted in the discovery of such elements, or such an amount of annual parallax, or sidereal displacement, as an actual change of position of a few feet will produce. It is useless to say, in explanation, that this very minute displacement, is owing to the almost infinite distance of
the fixed stars; because the very same stars show an equal degree of parallax from a very minute base line; and, secondly, it will be proved from practical data, in a subsequent chapter, that all the luminaries in the firmament are only a few thousand miles from the surface of the earth.
69:1 The barrel containing a spiral spring, so that the projecting force will always be the same, which might not be so with gunpowder.
77:1 "South Sea Voyages," p. 14, vol. i. By Sir James Clarke Ross, R.N.
83:1 Sir John F. W. Herschel, Bart., in "Good Words."
