DEPARTMENT OF LANDS AND FORESTS FOR 1928 75 



of this traverse line was check chained with a view of eliminating as far as possible 

 any error in chainage. Owing to the reliance that can be placed upon this checked 

 control traverse, it can be used as a base for fitting the blocks more accurately 

 to their relative positions. 



The actual survey of this ground control was carried out by transit, chain 

 and level, with automobiles serving as conveyances to and from the work, except 

 in a few cases where canoes or motor boats were required. However, later on 

 the topographical survey party will complete the operation with plane table, 

 barometers and other instruments that may be necessary. 



Transit and Tape Traverse 



All angles were measured by the transit and all distances by steel tape. 



The custom adapted was to set up the instrument at the angle point or 

 station, then setting the vernier at the corrected bearing of the last course with 

 the instrument sighting on the back picket or station and then by transiting 

 the barrel of the instrument and sighting on the station ahead the bearing for 

 the forward course may be read direct. This original bearing was recorded and 

 used as check for gross error. The corrected bearing was calculated by taking 

 the mean of the sum of the four interior angles at that angle point of the traverse 

 and from your last corrected bearing you will be able to calculate your corrected 

 bearing for the forward course. 



Frequent observations for azimuth were taken from time to time throughout 

 the survey. 



All distances between angle points or stations were measured by steel tape 

 three hundred feet in length, with all the slopes measured by clinometers. 

 Thermometers were carried to record the temperature at different times of the 

 day, and the correction applied, as well as great care was exercised as regards 

 the tension or pull on the chain as well as keeping the proper alignment. 



The allowable error of closure of all blocks, both as regards the instrument 

 work and chainage, was one in five thousand (1/5000) or approximately one foot 

 to the mile. Where it was found necessary to run a spur line only, the circuits 

 not being completed, all traverse angles were checked, if it was impossible to 

 get an observation, as well as all the distances between stations were rechained. 



Wherever we had the advantage of having the photographs in advance of 

 the survey, the chainmen carried the pictures in the field, marking upon them 

 in their proper positions all transit station, control points or any other infor- 

 mation that would be valuable in ascertaining the scale of the picture. This 

 method appeared very satisfactory, as it is much easier to interpret the objects 

 in the photograph when viewing the originals of these objects on the ground. 



Level Party 



The level party followed generally along the lines of traverse except in a few 

 cases where a nearby road was more convenient. The elevations of all lakes 

 within a reasonable distance of the traverse lines were taken and recorded, as 

 well as the levels of all bridges, culverts and watercourses. The precise levels of 

 different -points along the railways, of which we had a record, were taken advan- 

 tage of as checks against our own elevations. The allowable error in levelling 

 was one-tenth of the square root of the distance in miles. 



