CHAP. II.] A INIARINE SURVEY IN GENERAL 63 



The accuracy necessary in many details of a chart depends Accuracy 

 very much upon its scale. Over-accuracy is loss of time. sary. 

 Any time spent in obtaining what cannot be plotted on the 

 chart is, as a rule, loss of time ; but it cannot be too strongly 

 impressed upon the young nautical surveyor, that liis work 

 should be as correct as his scale ^\'ill allow. Nothing should 

 be put down of which he is not sure, and it is no loss of time 

 to repeat angles to prevent mistakes. It is better to be over- 

 accurate than to err in the opposite direction, and experience 

 will soon show him when he must be very exact, and when 

 a little latitude is permissible without interfering with the 

 result. 



The accuracy of the main triangles of a chart is most im- 

 portant ; everything depends on them, and if they are incorrect, 

 nothing wiU be satisfactory afterwards. 



The general plan of a survey may be said to be this : — General 



1st. A base is obtained, either temporary, as in the case of survey. 

 an extended survey ; or absolute, as in a plan. This is the 

 known side of the first triangle. 



2nd. The main triangulation, that is, the establishment by 

 means of angles of a series of positions, at a considerable 

 distance apart, from which, and to which, angles are after- 

 wards taken, to fix other stations. These are the corners of 

 our framework, and are known as the " main stations," the 

 two ends of the base being the first two, on which everything 

 is built. 



3rd. The fixing by means of angles from these main stations 

 of a sufficient number of secondary stations, and marks, to 

 enable the detail of the chart to be filled in between them. In 

 most cases angles will be required to be taken from the marks 

 themselves as well. 



4th. All these points, or those embracing a sufficient area 

 to work on, being plotted on the chart, they are transferred 

 to the field boards, either by pricking through the plotting 

 sheet with a fine needle, or, what is a better way when care- 

 fully done, by making a tracing of them on tracing-cloth, and 

 pricking through that on to the boards. 



5th. Each assistant then has a certain portion told off to 

 him to do. It must depend upon circumstances, but as a 

 rule it is more satisfactory to have the coast-line put in first, 



