232 SCIENTIFIC APPARATUS. 



in proportion as instruments and maps were improved. Early 

 explorers by land were content with itineraries and maps which 

 only indicated distances, as the Pentinger tables. The observa- 

 tion of bearings by compass introduced an important improve- 

 ment; and after the invention of Hadley's quadrant, these 

 rough route surveys began to be checked and verified by astro- 

 nomical observations. Bruce, when he went to Abyssinia, took 

 with him a quadrant which it required three men to carry, and he 

 made excellent use of it ; and Major Rennell, in his survey of 

 Bengal between 1763 and 1782, measured his distances by chain, 

 and observed both for latitude and longitude at fixed stations. 



The modern traveller needs a good watch, a sextant, an 

 artificial horizon, an azimuth compass, a nautical almanac, and 

 tables. He must also be supplied with aneroids and boiling- 

 point thermometers, to enable him to construct a section of the 

 country he traverses, and delineate its principal physical features. 

 The maps constructed from materials so obtained are sufficient 

 for wild and little-known regions, and for countries a knowledge 

 of which is only needed for political or commercial purposes. 

 In this category by far the greater part of the earth may be 

 placed. Such maps are based on as many positions as possible, 

 which are fixed by astronomical observations, while the inter- 

 mediate country is delineated by careful traverses and route 

 surveys, and by plane tabling. But the charts of coasts, upon 

 which the safety of ships depends, cannot be prepared with too 

 close an attention to accuracy. Running surveys are not now 

 sufficient for frequented coasts, and important marine surveys 

 have long been executed on a trigonometrical basis. 



The scientific apparatus required for geographical work differs 

 according to the amount of accuracy required; and when 

 maps are called for, not merely for political, military, or com- 

 mercial, but also for administrative uses, the very highest degree 

 of accuracy is desirable, and has been attained. It is, con- 

 sequently, in the execution of cadastral surveys that the greatest 



