391 SURVEY OP THE COAST 



and always to repeat them aloud when he has written them, 

 to prevent mistakes ; and if he is attentive, and acquainted 

 by practice witli the proper succession of the readings, he 

 can, in cas(; of mistaken or improbable readings, by warning 

 the observer, cause the correction of any mistake, by a re- 

 petition of the reading before the instrument is moved. In 

 observations requiring tlie notation of the time, he will count 

 with the chronometer, and mark the moment when tlie word 

 is given to him by the observer. 



A second will act as an assistant observer in such obser- 

 vations as require it, observe regularly, at stated hours, and 

 at the time of every observation requiring it, the barometer 

 and thermometer, of which he will keep a regular journal, 

 make the observations of the magnetic needle, in cases where 

 it is of interest, as in the survey of a sea coast. 



A third assistant will find sufficient employment in preli- 

 minary calculations, the making of a second copy of the day 

 book, occasional attention to the signals, directing the men 

 in clearing views, and various similar occupations. 



One of the assistants should be a draughtsman for views, 

 who should draw on each station the view of the whole ho- 

 rizon, marking the positions of all the signals, so as to indi- 

 cate their place if they shoidd be needed at any future time. 

 The foreground of his drawing will also aid in finding the 

 station point itself. He will also make detailed drawings of 

 the signals, as they present themselves in the magnified 

 scale through the largest telescope, with all the other ob- 

 jects accom|)anying it in the field of the telescope. This 

 will direct the observer in distinguishing the signals in the 

 smaller telescopes of the instruments from other objects 

 which it might be easy to mistake for them. 



These drawings, which will form a pretty large collection, 

 may assist in the proper shading of tlic elevations in tl)e 

 drawing of the maps; and tliey may serve, il' circumstances 

 should make it desirable, to made a model in relief of a part 

 of the country, for which many of the mathematical data are 

 given in the survey, as the elevation of all the signals over 



