Method of conducting the Canal Surveys. 21 



In the investigation of the subject, it became apparent that one of 

 two modes differing materially from each other in their general prin- 

 ciples, must be adopted. 



The first method contemplated the measurement, in the usual man- 

 ner with the circumferentor and chain, of the outlines of the ground 

 occupied by the Canals, with such references to permanent objects 

 and cross measurements as were necessary for verifying the accuracy 



of the 



survey 



In the other method the location of the outlines or boundaries was 

 to be determined by offsets, made in a specified manner, from a base 

 line situated upon and coinciding with the inner edge of the towing- 

 path, the best defined, and, (as an object for general reference) the 

 most permanent part of the Canal. References were likewise to 

 be made as contemplated in the preceding method to all accessible 

 objects of a permanent character for verifying the accuracy of the 

 survey. 



This latter method being the one which received the sanction of 

 the commissioners and Canal board, its details will be more fully de- 

 scribed as follows. 



1 . The measurements in the direction of the length of the Canal 

 were made upon the base line above mentioned, situated upon or co- 

 inciding with the inner edge of the towing-path. The height of the 

 surface of the towing-path, and the inclination of its inner slope being 

 supposed the same as specified in the transverse profile adopted in 

 the construction of the Canals. 



2. The several changes in the direction of the base line were re- 

 fered to the magnetic meridian. The whole line being thus resolved 

 into as many separate alignments, as it contained portions having dif- 

 ferent courses or bearings. 



3. The several alignments were accurately measured in chains and 

 tenths ; (fractions other than tenths being avoided by a very little care 

 in arranging the stations) and the distances upon each to the several 

 points where the lines of roads, counties, towns, patents, lots, &c. in- 

 tersected the same, together with their courses or bearings, were care- 

 fully observed. 



4. The distances likewise to all waste-weirs and culverts, and to 

 all streams that discharged themselves into or otherwise intersected 

 the Canals were taken, and the same was done with respect to the 

 road and farm bridges, locks, aqueducts, &c. The distances to the 

 bridges were taken to the lines joining the two nearest angles or cor- 



