action by a fragment of zinc and a sixpence pressed against the tongue. The attempts to lay the cable in August 1857 failed through stretching it so tightly that it snapped and went to the bottom, at a depth of 12,000 feet, forty times the height of St. Paul’s. This great work was resumed in August 1858; and on the 5th the first signals were received through _two thousand and fifty miles_ of the Atlantic Cable. And it is worthy of remark, that just 111 years previously, on the 5th of August 1747, Dr. Watson astonished the scientific world by practically proving that the electric current could be transmitted through a _wire hardly two miles and a half long_.[55] Miscellanea. HOW MARINE CHRONOMETERS ARE RATED AT THE ROYAL OBSERVATORY, GREENWICH. The determination of the Longitude at Sea requires simply accurate instruments for the measurement of the positions of the heavenly bodies, and one or other of the two following,--either perfectly correct watches--or chronometers, as they are now called--or perfectly accurate tables of the lunar motions. So early as 1696 a report was spread among the members of the Royal Society that Sir Isaac Newton was occupied with the problem of finding the longitude at sea; but the rumour having no foundation, he requested Halley to acquaint the members “that he was not about it.”[56] (_Sir David Brewster’s Life of Newton._) In 1714 the legislature of Queen Anne passed an Act offering a reward of 20,000_l._ for the discovery of the longitude, the problem being then very inaccurately solved for want of good watches or lunar tables. About the year 1749, the attention of the Royal Society was directed to the improvements effected in the construction of watches by John Harrison, who received for his inventions the Copley Medal. Thus encouraged, Harrison continued his labours with unwearied diligence, and produced in 1758 a timekeeper which was sent for trial on a voyage to Jamaica. After 161 days the error of the instrument was only 1m 5s, and the maker received from the nation 5000_l._ The Commissioners of the Board of Longitude subsequently required Harrison to construct under their inspection chronometers of a similar nature, which were subjected to trial in a voyage to Barbadoes, and performed with such accuracy, that, after having fully explained the principle of their construction to the commissioners, they awarded him 10,000_l._ more; at the same time Euler of Berlin and the heirs of Mayer of Göttingen received each 3000_l._ for their lunar tables.