are still used, they are now defined in terms of the metre – for example the yard has since 1959 officially been defined as exactly 0.9144 metre. Universal measure The standard measures of length in Europe diverged from one another after the fall of the Carolingian Empire (around 888): while measures could be standardised within a given jurisdiction (which was often little more than a single market town), there were numerous variations of measure between regions. Indeed, as the measures were often used as the basis for taxation (of cloth, for example), the use of a particular measure was associated with the sovereignty of a given ruler and often dictated by law. Nevertheless, with the increasing scientific activity of the 17th century came calls for the institution of a standard measure or "" (as Italian Tito Livio Burattini said), which would be based on natural phenomena rather than royal decree, and would also be decimal rather than using the various systems of subdivision, often duodecimal, which coexisted at the time. In 1645 Giovanni Battista Riccioli had been the first to determine the length of a "seconds pendulum" (a pendulum with a half-period of one second). In 1671 Jean Picard measured the length of a "seconds pendulum" at the Paris Observatory. He found the value of 440.5 lignes of the Toise of Châtelet (a [English: fathom] is defined as 6 [foot] or 72 [inches] or 864 [lines]), which had been recently renewed. He proposed a universal toise (French: ) which was twice the length of the seconds pendulum. However, it was soon discovered that the length of a seconds pendulum varies from place to place: French astronomer Jean Richer had measured the 0.3% difference in length between Cayenne (in French Guiana) and Paris. Jean Richer and Giovanni Domenico Cassini measured the parallax of Mars between Paris and Cayenne in French Guiana when Mars was at its closest to Earth in 1672. They arrived at a figure for the solar parallax of 9.5 arcseconds, equivalent to an Earth–Sun distance of about 22,000 Earth radii. They were also the first astronomers to have access to an accurate and reliable value for the radius of Earth, which had been measured by their colleague Jean Picard in 1669 as 3,269,000 . Isaac Newton used this measurement for establishing his law of universal gravitation. Picard's geodetic observations had been confined to the determination of the magnitude