48 HYDROGRAPHICAL SURVEYING [chap. i. 



properly placed, to be able to altogether do away with putting 

 up his own marks for the details of the survey, and it is of these 

 we now speak. 



White- Whitewash is the great friend of the surveyer. It has 



wash. ^j^g advantage of being portable, showing generally very 

 well, being cheap, and obtainable all over the world ; it cannot 

 disappear by being blown over, or by being stolen or knocked 

 down by jealous inhabitants, who very naturally do not under- 

 stand what the meaning of different objects dotting their 

 shores may be. Whitewash, therefore, is used wherever 

 practicable, as on rocky cliffs and points, or tree-stems, angles 

 of houses, etc. ; and is also used to whiten other objects put 

 up by the surveyor, as cairns, canvas, etc., where either there 

 is no solid substance to whitewash, or it is necessary to see the 

 mark from every direction, which it is evident cannot be the 

 case when a cliff face is whitewashed, for example. 



The nature of these marks must vary according to locality, 

 and the distance it is necessary to see them. 



Cairns. Where there are stones, nothing is better than a cairn. 



It is rather a question as to whether a cairn on a hill-top is 

 better whitewashed or not. If the sun strikes on it, or there 

 are higher dark liills behind, it shines like a star ; but on a 

 dull day, against the sky, a white cairn will be so much the 

 colour of it, that a dark object will show better. 

 A cairn on the beach should certainly be whitened. 



Tripods. Where there are no stones, tripods of rough poles or stakes, 

 about 8 feet long, round which a bit of old canvas about 6 feet 

 long, whitewashed, can be laced with spun-yarn, will be found 

 good. The poles are easy to carry in the boat, and can be 

 taken up hills without difficulty ; they are easily taken down, 

 and can be used over and over again. From their tripod form, 

 they stand well in high wind, though it is as well to give them 

 spun-yarn stays. The conical shape of the mark affords a 

 capital object, and rough poles of the kind required can be got 

 anj^vhere. 



Where bamboos can be got they are very useful, from their 

 lightness, to carry up hills, either to form tripods as just 

 described, or as flag-poles. 



Pieces of wide coarse white calico are useful for temporary 

 marks, as where it is desired to see a station from another 



