236 SCIENTIFIC APPARATUS. 



angulation, by means of which the boundaries are fixed, and topo- 

 graphical details are rilled in by the topographical and revenue 

 surveyors, under the Surveyor-General; the former working in the 

 wilder and more thinly-peopled tracts, and in the native states, 

 and the latter in populous districts where, for administrative 

 purposes, minute accuracy is essential. 



As in Great Britain and India, so in all the Christian nations 

 of Europe, in the United States, and in some of our colonies, 

 trigonometrical cadastral surveys have been undertaken with a 

 view to the supply of rigorously accurate maps for statistical and 

 for numerous administrative uses. 



Thus the scientific apparatus required for the several classes 

 of geographical and geodetic operations, varies in proportion 

 to the degree of accuracy required. For the ordinary work of 

 navigation, and for the execution of running surveys of newly- 

 discovered coast lines the sextant, chronometer, sounding lead and 

 line, and compass suffice. But for the preparation of charts of 

 much frequented seas and channels the marine surveys must be 

 executed on rigorous trigonometrical principles. In the same way 

 on shore, the explorer of an unknown country need only make a 

 careful traverse, with a section, and points fixed at intervals by 

 astronomical observations with the sextant and artificial horizon. 

 For political boundaries of semi-barbarous countries, military 

 reconnaissances, and more frequented routes, somewhat greater 

 accuracy is needed. In Persia, Major St. John carefully measured 

 the distances with a perambulator, ascertained the longitude by 

 the use of the electric telegraph, besides taking the usual observa- 

 tions with the sextant. But when very accurate maps are needed, 

 the geodetic instruments are used which are capable of giving 

 exact results, and only errors of a few inches are admissible in as 

 many hundreds of miles. 



CLEMENTS R. MARKHAM. 



