Prime meridian

• Publisher: Elsevier Science
• Year: 1879
• Tongue: English
• Weight: 62 KB
• Volume: 107
• Category: Article
• ISSN: 0016-0032
• DOI: 10.1016/0016-0032(79)90499-x

✦ Synopsis

Reversal of MotionWithout.Gears or Belts.--In 1853, MM. Claparade, Roux and Delille attempted to produce opposite revolutions in two parallel arbors by means of a Watts parallelogram, but these experiments were not satisfactory. Charles Bourdon has lately intro-<tuced a contrivance which is based upon the two following theorems : 1. If two cranks, of any length and initial position, turn with the same angular velocity, the point which divides the line of variable length, which joins their extremeties at each instant, describes a straight line parallel to the bisectrix of the angle of the two cranl~s. 2. When the two cranks are equal, the projection of the joining line on the bisectrix preserves a constant length. By means of an ordinary slide, M. Bourdon compels the middle of the system to take a rectilinear movement. Then, by means of two reciprocating Peaucellier cells, or even without the use of cells, if one extremity of the crank is allowed a :slight play, two arbors may be easily connected so as to turn in opposite directions and to avoid any dead point.--Bull, de la Soe. d'~cour.

C. Prime Meridian.--The ancient geographers knew nothing west ~)f the Fortunate or Canary Islands. Ptolemy started from that point to estimate longitude, going eastward to the extremity of the countries which were then known. According to his geography, Paris would have had a longitude of about 23½ °. In 1682 the :French geographers generally estimated the longitude at 20 ° , but some writers fixed upon 23½ ° , 22½ ° and 20½ ° . England subsequently adopted the meridian of St. Paul, in London~ and afterwards Greenwich. :France, in 1789, adopted the meridian of Paris. These, examples havebeen followed by Holland, Spain, Portugal, Russia, United States, Chili and Brazil, each country adopting either its own capital or its principal observatory as the zero point of longitude. In order to remedy the confusion arising from these various meridians, M. de Chancourtois proposes to take the meridian of St. Michel, in the Azores, which agrees closely with that of Ptolemy and that of Mercator, and which seems to have other advantages, because it passes entirely through the ocean for one-half of its extent, and on the other half it onl): cuts the eastern extremity of Asia, thus separating pretty exactly the old and the new worlds. Bouthillier de Beaumont and E. Corlanbert propose an initial meridian ten degrees east of Paris, and that Italy and the United States should cede to the Republic of Science neutral stations for observatories upon that meridian.~La 2~ture.

C.