“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 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! [BEGGING THE QUESTION, CIRCULAR REASONING, AD HOC REASONING, HITCHEN’S RAZOR, AFFIRMING THE CONSEQUENT FALLACIES; DO I NEED TO ADD MORE?-DS]
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
on 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 a 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;” 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;”
Zetetic Astronomy, by ‘Parallax’ (pseud. Samuel Birley Rowbotham),