4o8 Report S.A.A. Advancement of Science. 



The supply pipe is controlled 1»y a valve from the outside ,and 

 on the inside a galvanized wrought pipe is connected thereto by 

 means of a tninion joint, which admits of the pipe being raised or 

 lowered by means of a crab winch so as to draw off the water as near 

 the surface as may be desired. These pipes are provided with gal- 

 vanized wire netting screens at the end, and when the pipes are 

 drawn up to the vertical position these screens can be readily cleaned 

 or renewed. 



Cost. — The following particulars of cost of actual construction 

 are given as a fair average over the seven dams which have been 

 constructed by the Department: — 



Sand-washed 5s. 6d. per cubic yard. 



Rubble quarrying 4s. lod. per cubic yard. 



i-^" metal and I" shivers 8s. 7d. ])er cubic yard. 



Cement (local manufacture) ... 16s. 2d. per cask of 4A cubic ft. 



Tradesmen us. to 13s. per day. 



Labourers - 7s. per day., min. 



The total cost of concrete work, with about ^^ per cent, plum- 

 stones, as measured on completion of the dam. is found to average 

 abtjut 30s. per cubic yard. 



36._notp:s ox thk progress of survey opera, 

 tioxs ix south africa. 



Bv SiK David Gill. K.C.B., LL.D., F.R.S., Hon.F.R.S.E. 



[not rKJXTED]. 



