888 PROCEEDINGS OF SECTION J. 



Ordinary poles or ranging* rods should not be used for 

 observing on account of their size and the difficulty of 

 keeping them exactly pei'pendicular ; in lieu of them what are 

 technically known as tripods are most convenient. These 

 consist of a fine metal bar swinging in an upright position on 

 gimbals at the top of a very light tripod stand, and kept 

 truly vertical above any point by a plummet suspended from 

 its lower end ; for long sights a carefully turned jjiece of 

 wood can be slipped on to the top of the bar. 



The measurement of the traverse line of the standard 

 survey must be conducted with great care. I should re- 

 commend the use of a 66 feet Chesterman's steel band, 

 4 inch wide and divided to tenths of links. In order to 

 ascertain the length of the band used, a standard should be 

 laid down in some convenient locality ; but its actual length 

 when used for chainage as regards its relation to the 

 trigonometrical standard is Ijest ascertained by measuring and 

 remeasuring between two stations of the triangulation, the 

 coordinates of which are of course known. The actual 

 length of the steel band itself cannot well be altered, but as 

 the expansion of a 66 feet steel band is '01 inch for every 

 2° Fahrenheit, it is easy to compute at what temperature it 

 is of true standard length. Different ingenious contrivances 

 have been devised, such as adjustable handles, &c. for altering 

 the length of the band itself, but I am not in favour of their 

 use. The band being almost invariably suspended in the 

 air wdien measurements are being made, the temperature can 

 be easily taken and noted from time to time as the survey 

 proceeds, the corrections for length being afterwards applied 

 in the office. When there is any slope the measurements 

 should always go down hill, so that the hind chainman holds 

 to the mark, never plumbing over it. The tape is kept 

 horizontal and free from vibration by a long grooved level 

 supporting it in the centre. The leading end is attached by 

 means of a spring balance to a sliding ring on an upright 

 movable pole, kept in jiosition by a plate at the bottom end 

 on which the chainman's foot is placed ; one tension, generally 

 10 lbs., is always kept up when chaining. A rather heavy 

 but very accurately centred plummet is suspended by a fine 

 line running through a small ring at the end of the band so 

 arranged that it can be raised and lov»^ered as required. The 

 leading chainman places the straining pole in line as directed 

 by the hind chainman ; he then slips the brass ring to the 

 correct height on it as indicated by the man with the level at 

 the centre, and the surveyor places a small metal plate under 



