35 



effect of refraction, and introduced corrections for both. 

 He may justly be termed the founder of the modern astronomy 

 of precision. 



He was succeeded by the Rev. NATHANIEL BLISS (1700- 

 1765), who, however, only survived him by three years, and 

 on May 7, 1765 NEVIL MASKELYNE (1732-1811), who had 

 already made the improvement of the practical business of 

 navigation his chief aim, was appointed in his place. None 

 of all the Astronomers Royal kept the original charter of 

 the office " to find the so-much desired longitude at sea 

 for the perfecting the art of navigation " so closely before 

 him as did Nevil Maskelyne. 



The problem was solved in two ways. The offer by the 

 Government of the reward of 20,000 for a clock or watch 

 which could keep its rate so perfectly at sea that the navigator 

 might, at any moment, learn the true Greenwich time from 

 it, had brought out the invention of the Chronometer by 

 JOHN HARRISON (1693-1776), and the method of lunar dis- 

 tances suggested 130 years earlier by Morin, and fraudulently 

 claimed as his own by Le Sieur de St. Pierre in 1674, had now 

 become practicable. For Bradley 's places of the stars 

 possessed the needful accuracy, and the lunar tables, pre- 

 pared by TOBIAS MAYER (1723-1762), and published in 

 London under Maskelyne's direction in 1770, gave the means 

 for predicting the place of the moon. 



Before his appointment to Greenwich, Maskelyne had 

 undertaken a voyage to St. Helena, in which he had given 

 the method of " lunars " a very thorough testing and found 

 it satisfactory. Part of its success was due to the improve- 

 ment by JOHN HADLEY (ob. 1744) of the instrument chiefly 

 used at sea, the Octant, as it then was, the Sextant as it became 

 a little later. 



In 1763 Maskelyne published the British Mariner's Guide, 

 a Handbook for the Determination of the Longitude at Sea by 

 the Method of Lunars ; and in 1765 he published the first 

 number of the Nautical Almanac, together with a volume of 

 Tables Requisite to be Used with the Nautical Ephemeris, the 

 value of which was so instantly appreciated that 10,000 

 copies were sold at once. The preparation and publication 

 of the Nautical Almanac was continued by Maskelyne up to 

 his death in 1811. 



To Maskelyne, therefore, we owe the first practical solu- 

 tion of the problem of determining the longitude at sea, 

 and the method was promptly put into use by men of remark- 

 able energy and skill. Of these, one was CHARLES GREEN, 



c 2 



