1836.] 



Irrigation of the Delta of Tanjore. 



319 



Colleroon and Cauvery are both used for traffic to a very considerable 

 extent; cotton, piece goods, saltpetre, sandal-wood, &c. are brought 

 down from Coimbatore and Salem, and conveyed to the ports of Nagore 

 and Porto Novo; but, as lines of communication, these rivers are com- 

 paratively of little use on these accounts ; first, they are extremely 

 shallow in general, and can only be navigated during the freshes, which 

 are very uncertain, and seldom continue many days together, even 

 during the S.W. and N.E. monsoons, and for many months in the year 

 they are not navigable at all; second, in consequence of the current, 

 and the want of a tracking path, it does not answer to carry goods up 

 these rivers, and even very few only of the empty boats are taken back, 

 so great is the labour of tracking or pulling against the stream, the 

 greater part of the boats which are all circular baskets from nine to 

 fourteen feet diameter, covered with buffalo leather, are taken to pieces 

 at the ports, the leather packed up and conveyed back on bandies or 

 men's heads, and the baskets abandoned. It is perhaps not quite cer- 

 tain that it would not answer to convey goods up the rivers ; perhaps it 

 is that the natives have not energy enough for such a traffic, but proba- 

 bly it would not be very greatly cheaper than land carriage. The 

 advantage that the canal will have over the rivers, is, first, that by 

 means of the annicut it will be kept regularly supplied with water, as 

 long as there is any in the Colleroon, that is frequently during eleven 

 months, and seldom less than ten, out of the year; second, as it will 

 have a tracking path, it may be used for the conveyance of goods up as 

 well as down ; the current will vary from one to two miles an hour. 

 As a continuation of this a cut of seven miles long has been ordered, to 

 connect the Yellaur with the Cuddalore backwater, by which the water 

 communication will be completed to within eleven or twelve miles of 

 Pondicherry, and it is hoped that, at a comparatively trifling expence? 

 cuts may be made to connect the different backwaters as far as Madras, 

 from whence, by Cochrane's canal and the Pulicat lake, the communi- 

 cation is already open nearly to Nellore. 



V. — On a method of using Sir Howard Douglas's Reflecting Semicir- 

 cle in Military Sketching. — By Lieut. J. Campbell, Asst. ibur. Genl. 



The method of using this instrument in military sketching, for the 

 protraction of the place of a point by the angles subtended by it from 

 two other known stations, is well known, but in this way the instrument 

 can only be used in making small sketches of a camp, or of a proposed 

 encamping ground, or of a fort, &c. where the extent is small, and the 

 arms of the instrument are long enough to protract the observed angles 



