132 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



the latitude of Portsmouth, an amount well within the limit of 30 

 miles specified for the grand prize of the longitude commission. 



Apparently Harrison had won the prize of nearly $100,000.00; but 

 the invention of the sextant, which had helped Harrison by facilitat- 

 ing the determination of local time, had been especially favorable to 

 certain powerful competitors who hoped to gain the reward by meas- 

 urement of lunar distances from stars. Much improved lunar tables 

 had been submitted by Mayer in 1755. These were pronounced gen- 

 erally correct within a minute of arc; and Maskelyne, after a trial 

 voyage to St. Helena in 1761, during which he determined longitudes 

 within 90 miles or so, prepared a guide, issued in 1763, in which he 

 asserted his belief that the lunar method would determine longitudes 

 always within 60 geographical miles on the equator and generally 

 within 30 miles, if applied to careful observations. Encouraged by 

 this progress, though the process involved was too laborious for sea- 

 men to undertake, the House of Commons withheld the prize from 

 Harrison and left an open chance for a lunarian during four years 

 from 1763. 



In March, 1764, on another trial voyage to the West Indies, Har- 

 rison's watch made a record even better than before, running four 

 months with an error not greater than 10 geographical miles in 

 longitude. Accordingly in the following year he was awarded one- 

 half of the prize of £20,000; but at the same time, authority and 

 funds were given for the publication of the Nautical Almanac, con- 

 taining among other things tables of the moon's distance from the 

 sun, when suitable, and from seven fixed stars at intervals of three 

 hours. Apparently the longitude commissioners were still in doubt. 



The tables of lunar distances in the Nautical Almanac, together 

 with Maskelyne's auxiliary tables, facilitated greatly the lunar 

 method for finding longitude. But steady progress toward the per- 

 fection of the chronometer maintained the superiority of the chrono- 

 meter method of longitude determination, and soon after 1800 the 

 longitude controversy may be considered to have been settled in favor 

 of the accurate timepiece. 



The marvelous accuracy of the modern chronometer — of even the 

 cheaper chronometers used in the mercantile marine — is illustrated 

 by the steamship Orellcvna sailing from London to Valparaiso. In a 

 voyage of 63 days the mean accumulated error of her three chrono- 

 meters was only 2.3 seconds of time, or six-tenths of a mile in longi- 

 tude at the equator, and less in higher latitudes. 



At the present time, since the Greenwich time can be sent out by 

 wireless from shore stations, in the problem of longitude determina- 

 tion even less dependence need be placed on the chronometer, and the 

 accuracy of such determinations is not necessarily appreciably dif- 

 ferent from that of latitudes. 



