eeOGRAPHICAL AND TOPOGRAPHICAL IMPROVEMENTS. gQS 



fefs a complete knowledge of its furface. In war, fucK know- 

 ledge is abfolutely neceffary for defence; in peace, for im- 

 proving the country to the beft advantage. 



Now, iince geography may be improved, an eafy and ac- Utility of acor- 

 curate method io lay down maps of mountainous countries J^ l^jf '""^°" 

 and hilly eftates, will perhaps prove ufeful, as it will (how at 

 a (ingle view the true Ihape and comparative height of the 

 ground without the art of painting. 



As mountains are apt to eclipfe each other, a perfpe^ive Mountains can- 

 view is feldom very extenfive, the rules of which fall ^^ort 2,°^^^ "^^^ " { 

 of giving an accurate idea of any hilly country; becaufe fuch fpeftive, 

 a view, though ftri<5lly true in one particular place, is not fo 

 in any other. The altitudes of mountains appear in proportion 

 to the diftance from the eye, and no rule in geometry has been 

 found fufficient to determine diftances from any fingle ftation. 

 Neither can a bird's-eye view of an eftate afcertain the depth 

 of valleys or the height of mountains. But the method here 

 propofed will be found equally capable of giving the true fliape 

 of any ground above or below water. It may be fuccefsfully 

 applied to fea charts, and will prevent much confufion, arifing 

 from the tedious method of diftinguiftiing foundings by a mul- 

 titude of figures. 



Explanation. 



Suppofe a full defcription is required of any ifland in the New methodi 

 ocean. Firft, let an accurate map be laid down in the com-^^^^ ^ S^od 

 mon way; and let the perpendicular height between the high-M^rk the point 

 efl: point of land and the ocean be divided into any number of°^ higheftele- 

 equal parts. Suppofe thefe equal divifions are 100, 200, 300, pofo^" d?ffe°ring'' 

 400 feet above the low-water mark. From the different in elevation by 

 points of thefe feveral divifions, let horizontal lines be run ^"^'^^ [?^eafures. 

 With a good theodolite, and ipint level annexed, all round the theodolite 

 the ifland. If the work is well done, each line will end where a"d 'cvel from 

 it began; and if the bearings and difiances of thefe feveral which if the' 

 lines are truly laid down on the map, the crooked courfes of^^^^^Y ^(^s^o^f 

 them will clearly fliow the fliape of the ground over which they terminate!^^^'* 

 pafs. For example : if any horizontal line pafles by the fide Thefe lines laid 

 pf a'fteep hill, it will incline towards the ocean, or approach ftJ^'ihTfigrr" 

 ti)e next horizontal line below it. When the fame line crofTes of the country. 

 a ftream of running water or a valley, it will naturally bend 

 np the fide of the faid flream, until it cancrofs it without lofing 



the 



