Curiosities of Science. 



JttteceHattea. 



HOW MAKINE 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."* (Sir David Brewster' s Life of 

 Newton. ) 



In 1714 the legislature of Queen Anne passed an Act offer- 

 ing a reward of 20,000. 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, Har- 

 rison 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 instru- 

 ment was only l m 5 s , and the maker received from the nation 

 5QOOL The Commissioners of the Board of Longitude subse- 

 quently 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 accu- 

 racy, that, after having fully explained the principle of their 

 construction to the commissioners, they awarded him 10,000. 

 more ; at the same time Euler of Berlin and the heirs of Mayer 

 of Gottingen received each 30001. for their lunar tables. 



* Newton was, however, much pestered with inquirers ; and a Correspondent 

 of the Gentleman's Magazine,, in 1784, relates that he once had a transient view of 

 a Ms. in Pope's handwriting, in which he read a verified anecdote relating to the 

 above period. Sir Isaac being often interrupted by ignorant pretenders to the 

 discovery of the longitude, ordered his porter to inquire of every stranger who 

 desired admission whether he came about the longitude, and to exclude such as 

 answered in the affirmative. Two lines in Pope's Ms., as the Correspondent re- 

 collects, ran thus : 



" ' Is it about the longitude you come?' 

 The porter asks : ' Sir Isaac 's not at home.' " 



