GEOGRAPHICAL INSTRUMENTS. 23, 



astrolabe, the rule for applying declination, rules for dead 

 reckoning, and for longitude. Latitude was obtained by observa- 

 tion, but longitude had usually to be reckoned on the chart from 

 the meridian of the Canary Islands, which in those days was used 

 by all civilised countries. The difference of time between the 

 eclipses of the moon at the place of the observer, and the place 

 for which it was calculated in the ephemerides of that day was 

 another method in use, for finding the difference of longitude. 

 Mariners were also provided with tables, giving the number of 

 miles in a degree of longitude, for every degree of latitude. 



By means of these rough instruments and calculations 

 our Elizabethan navigators, and their contemporaries in Spain, 

 Portugal, France, and Holland succeeded in delineating the 

 vast regions that were discovered, and thus increased the sum of 

 human knowledge, while men's minds were enlarged, and the 

 wealth and prosperity of nations were increased. 



The improvement of scientific apparatus naturally went 

 hand in hand with the progress of discovery. The great 

 desideratum was the means of finding the longitude ; and it was 

 the creation of a commission for the discovery of longitude in 

 1713, which, so far as this country is concerned, gave the greatest 

 .stimulus to inventions connected with geographical research. 

 To the Board of Longitude is due the conception of the Nautical 

 Almanac, and the establishment of a surveying branch of the 

 naval service. The Nautical Almanac first appeared in 1767, 

 under the auspices of Dr. Maskelyne, the Astronomer Royal, 

 who, by furnishing tables of lunar distances, supplied another 

 means of finding the longitude. The invention of the quadrant, 

 for use at sea," in 1731, by Hadley, which entirely superseded the 

 astrolabe and cross-staff, in taking the altitude of heavenly bodies, 

 was a still greater improvement; and it was soon followed by 

 better instruments on the same principle the sextants of Dollond 

 and Troughton, 



The work of travellers on shore also became more accurate 



