20 Comparison of the Indus and Ganges Rivers. [Jan. 



fixed one. And if the survey be hastily executed, he will probably find 

 the general direction of the line, as given by his protraction, to be con- 

 siderably at variance, with that connecting the two fixed points. To 

 divide the error, which is generally in excess, proportionally among the 

 smaller lines of the protraction, according to the principles of geometry ; 

 or in fact, to make the route fit in between the two fixed points, is our 

 present purpose. 



Let AB then (Plate II. fig. 2) be the two fixed points on a map ; 

 and Afl, ab, be, cB', the protracted route. (The error is apparent ; in 

 the general direction, as much as the angle BAB'; and in the direct 

 distance, too much by the quantity B"B\) First, draw lines from A 

 to each bend in the route, as A«, A6, and Ac. Then on the line AB' 

 lay off AB" equal to the true distance AB. Now, parallel to B'c from 

 B", draw the line B'V, and observe where it cuts the line Ac ; make a 

 mark, and call that point c' : then parallel to cb, draw c'6', and where 

 it intersects the line Kb, mark the point 6' ; proceed similarly till you 

 find the point a\ Join Aa', a'6', b'c\ and c'B", and the route is reduced 

 to the true distance. But we have yet to transfer this to the line AB : 

 for this purpose, take Aa', A6', Ac', each as radius in your compasses, 

 and from the points «', V, c', describe arcs cutting both the lines AB", 

 and AB, in the points 1, 2, 3, and 1', 2', 3'. Lay off the distances la', 

 26', 3c', on the arcs from 1' to «", 2' to 6", and 3' to c" : lastly, draw 

 the lines Aa", a"6", b"c",c"B, and the route is duly transferred. 

 This method also admits of applying correction, where the protraction of 

 the route falls short of the true distance. 



Calcutta, 28th Nov. 1831. J. G. 



VIII. — Comparison of the Indus and Ganges Rivers. 

 Lieutenant A. Burnes, Assistant Resident in Cutch, who lately com- 

 municated to the Bengal Government a geographical report upon the 

 Indus, drawn up from notes and surveys made on his recent mission to 

 Lahore, estimates the magnitude of the Indu?, at Tatta, a place situated 

 equidistant from the ocean with Sikrigali ou the Ganges, as four times 

 greater than the latter river, upon the estimation given in the Glean- 

 ings, III. 185, in the month of April : but it may reasonably be doubt- 

 ed, whether the discharge of water in the Ganges is not underrated at 

 21,000 cubic feet per second at Sikrigali, since the same quantity is also 

 estimated to flow past Benares, and that upon more accurate data, at 

 the same season. Lieutenant Burnes thus states the chief data of the 

 comparison. 



