Meridian

“ The theory that the prime meridian is a matter purely of a geographical nature is liable to the fatal objection that the determination of the difference of longitude between one place and the other is really the determination of the difference of time of the passage of a star across the meridian of the two places concerned. That is very definite. You observe the transit of the star at one place, and you observe the transit of the star at the other place, and by means of telegraphic communications you are able to determine their difference of longitude independent of the figure of the earth. ”

“ Whatever we may do, the common prime meridian will always be a crown to which there will be a hundred pretenders. Let us place the crown on the brow of science, and all will bow before it.
Commander Sampson, Delegate of the United States, said that he thought that the Delegate of France, Professor Janssen, had explained very fully the advantages of a neutral meridian, but he thought that he had not explained how we are to determine the neutral meridian. ”

“ Each elliptical meridian has for one axis the central meridian, and for the other the intercepted portion of the equally divided equator. It follows that the meridians 90° east and west of the central meridian form a circle. It is easy to show that to preserve the property of equal areas the distance of any parallel from the equator must be √2 sin δ where π sin φ = 2δ + sin 2δ, φ being the latitude of the parallel. The length of the central meridian from pole to pole = 2 √2, where the radius of the sphere is unity. The length of the equator = 4 √2. ”

“ Longitude is the distance of the meridian of any place from the meridian which passeth over the Isles of Azores, where the beginning of longitude is said to be. The meridian is a great circle dividing the Equinoctial at right Angles into two equal parts, passing also through both the Poles, and the Zenith, to which circle the Sun coming twice every 24 hours, maketh the middle of the day, and the middle of the night. Every place hath a several meridian, but they all meet in the poles of the world. Latitude is counted from the Equinoctial to the end of 30 degrees on each side thereof. ”

“ The sun, moving along the ecliptic, always moves in a great circle, while the point of the meridian which is to overtake the sun moves in a diurnal circle, which is sometimes a great circle and sometimes a small circle. When the sun is at the equinoxes, the point of the meridian which is to overtake it moves in a great circle. As the sun passes from the equinoxes to the solstices, the point of the meridian which is to overtake it moves on a smaller and smaller circle: hence, as we pass away from the celestial equator, the points of the meridian move slower and slower. ”

“ The true meridian may also be ascertained, or rather the equinoctial line, which cuts the meridian at right angles, by observing the points where the sun rises and sets, and by observing how much they are distant from the equinoctial either to the north or to the south. For this purpose an astrolabe is formed with the globe; that is, a circle is made representing the earth’s circumference, divided into 360 deg. ”

“ When the 21st of March comes around again, and the meridian presents itself to the sun and the First Point of Aries in range, a careful count of the number of times this latter point has crossed the meridian during the year, discloses 3661⁄4 transits. That is, the earth has actually turned about its axis 3661⁄4 times. The sun is found to have passed the meridian only 3651⁄4 times. Counting the rotations of the earth by the number of the sun’s transits while we are revolving around him, causes the apparent loss of a day due to the earth unwinding itself once, so to speak, during the year. ”

“ In the face of this difficulty, which appears to me insurmountable, the only solution which, by its very nature, will not raise exciting questions of national pride is that of a meridian having a character of absolute neutrality. If the adoption of such a meridian was admitted in principle, I am certain that a discussion based upon pure science, and following the best conditions which it should realize, would conduct us rapidly to a practical settlement of the question. ”

“ If the meridian were a perfect circle the change of zenith distance of the star, as one traveled along a meridian from the equator to the pole, would be perfectly uniform—the same number of degrees for each hundred miles traveled—and observations made in many parts of the earth show that this is very nearly true, but that, on the whole, as we approach the pole it is necessary to travel a little greater distance than is required for a given change in the angle at the equator. ”

“ It has been shown that meridians are, necessarily, straight lines; and that it is impossible to travel round the Earth in a north or south direction: from which it follows that, in the general acceptation of the word “degree,”—the 360th part of a circle—meridians have no degrees: for no one knows anything of a meridian circle or semicircle, to be thus divided. But astronomers speak of degrees of latitude in the same sense as those of longitude. ”

“ We may then say that, from a purely scientific point of view, any meridian may be taken as the prime meridian. But from the standpoint of convenience and economy there is undoubtedly much room for a choice. ”

“ The prime meridian passes through longitude 0°. Sometimes designated TRUE MERIDIAN to distinguish it from magnetic meridian, compass meridian, or grid meridian, the north-south lines relative to magnetic, compass, or grid direction, respectively. A fictitious meridian is one of a series of great circles or lines used in place of a meridian for certain purposes. ”

“ Do you want a striking example of what differentiates a neutral meridian from a national meridian? In order to avoid the confusion which existed in geography at the beginning of the seventeenth century, on account of the multiplicity of initial meridians then in use, a congress of learned men, assembled in Paris at the instance of Richelieu to select a new common meridian, fixed its choice on the most eastern point of the Island of Ferro. ”

“ We should change the chronological reckoning which is now in vogue, and I contend that we have no right, scientific or historical, to make that change now. According to my views, the meridian of longitude is relatively an unimportant affair. It is a practical one; it cannot be changed in twenty years, probably, and it will take that time to correct all existing charts. But if you adopt a meridian for time, it will be very difficult to alter it in the future. ”

“ As the rotation of the planet swings it round, it passes the central meridian of the disk simultaneously throughout its length, and at that moment comes out so strikingly straight it seems a substantialized meridian itself. ”

“ Whatever that meridian might be, we must always assume for it a certain number of degrees from the capital of the country, where the place to be determined is located, and then take that imaginary meridian instead of a real point on the surface of the globe. ”

“ As the mariners’ compass points north and south at one and the same time, and a meridian is a north and south line, it follows that meridians can be no other than straight lines. But, since all meridians on a globe are semicircles, it is an incontrovertible proof that the Earth is not a globe. ”

“ On most terrestrial globe maps meridian circles are represented at intervals of ten, twenty, or thirty degrees, the prime meridian on which the degrees of latitude are marked being usually made very conspicuous, and to the close of the period under consideration usually made to pass through the Cape Verde Islands or the Canaries, a point always to be carefully noted in attempting to get a reading for the longitude of any particular place. ”

“ To find the meridian line by means of the pole star is a simple and accurate method, as a value can be obtained at 70 any time at night by a simple altitude, provided the time of observation is known. ”

“ To find the Meridian:—When two, or any number of fixed stars, which have the same right ascension, appear in a right line (or right circle) , and perpendicular to the horizon of any observer, if a right line be drawn on the earth's surface, or on any plane parallel to that horizon, and perpendicular to the line of fixed stars which is then perpendicular to that horizon, the right line so drawn will give, accurately, the meridian line of that observer. ”

“ Marking off on each of these parallels or arcs both to right and left a distance representing five degrees of the earth’s longitude, he thus established the points through which to draw his meridians which marked the boundaries of each sector, leaving between the sectors equal spaces to be cut away should the sectors be used for pasting on the surface of a sphere. Every fifth meridian and every tenth parallel is drawn in black; the equator, the tropics, the polar circles, and the prime meridian are gilded. ”

“ The meridians extend from pole to pole, and it matters not what parallel you may be on, whether north or south latitude, your distance can always be measured to the Greenwich meridian in arc or time precisely as well as though you were on the exact parallel of Greenwich itself. ”