149 



Enough has been quoted to dispose of the first point ad- 

 vanced by Mr. Calder. 



2 and 3. Bush lines and meridian. — One would be led to 

 infer, from the statements made, that the prismatic compass, 

 or the compass attached to the theodolite, afforded the only 

 available method of obtaining the bearings or azimuths of 

 lines, whereas it ought to be taken for granted, as a matter of 

 course, that even in the case of a survey, based upon an inde- 

 pendent magnetic meridian, the initial line of the survey was 

 the only one observed by the compass, the bearing thus 

 obtained being transferred to the plate, and all subsequent 

 readings derived therefrom. To whatever meridian the work 

 is done, or from whatever source derived, whether compass or 

 astronomical, the veriest tyro must be aware that the bearings 

 are carried on by the theodolite, and that the proof of accuracy 

 is found in the extent of accordance in the closure, either 

 upon one of the lines of the survey in hand, or at a trigono- 

 metrical station. The argument advanced has therefore no 

 foundation either in theory or in practice. If it has been 

 in any degree the practice to make surveys by compass only, 

 it ought to be no matter for surprise if the discrepancies in 

 the various surveys are found to be startling. Still less should 

 those discrepancies be a matter for surprise when we have an 

 authoritative assurance that the most favourable results have 

 been obtained from such a process as running a line by com- 

 pass bearing to some large tree, and then, after transferring 

 the instrument by guess to a supposed corresponding point on 

 the other side, carrying on the line again by compass bearing ; 

 and this not only in an isolated case, but " a dozen or twenty 

 times in every mile." It is also urged that by the mysterious 

 correction of " compensation " the error " will generally not 

 exceed half-a-dozen yards in the mile." Admittedly, there- 

 fore, the error may in some cases be much greater ; but even 

 what is considered a favourable instance depends entirely 

 upon chance or luck. The errors, it is said, compensate each 

 other to a great extent ; but it needs hardly to be stated that 

 the errors may be all the one way — all in the same direction — 

 and then instead of the compensation of errors bringing the 

 net error down to " half-a-dozen yards in the mile," the error 

 may be increased indefinitely. 



4 and 5. Errors in maps. — The statements made under this 

 head only furnish an additional condemnation of the system 

 in force. If the surveys are not trigonometrically connected 

 and homogeneous, it is impossible to construct correct general 

 maps, and it need be no matter of surprise that the draftsmen 

 should have failed in the task assigned them, and that the 

 maps are inaccurate. The reconstruction of the maps could 

 only be undertaken, with any hope of placing them upon a more 



