398 SURVEY OF THE COAST 



within sucli limits as will not admit too great an influence of 

 tlie figure of the earth upon the reduction. 



After this observation, time tnay be allowed for dining, 

 attention being paid however not to miss the corresponding 

 altitudes of tlie afternoon, the time of which must be calcu- 

 lated approximately before hand 



Between tiiree and four o'clock the favourable time for the 

 observation of terrestrial angles may begin again, sometimes 

 a little later, seldom earlier. Tiiere will be little time to 

 lose, after the corresponding altitudes and the calculation of 

 their result, before it will be necessary to commence the 

 levelling of the theodolite, and the revision of all its adjust- 

 ments. 



The illumination will now become favourable for the sig- 

 nals in succession from due north past tlie east to about south 

 or somewhat farther, according to tlie declination of the sun, 

 as this forms the element of the angle of reflection from the 

 signals to the observer. By this it is also evident that the 

 time for accurate observations upon terrestrial objects be- 

 comes always more limited on both sides of noon, as the de- 

 clination of the sun becomes lower, and an attention to this 

 subject will have a great influence on the accuracy of the re- 

 sults. 



The order of the observations in terrestrial angles, azi- 

 mutlis, ^c. in the afternoon will be exactly the reverse of 

 that of the morning, except that though it was possible to 

 observe with and read on tlie instrument in the morning 

 before sunrise, this will not be possible after the sun is set. 



The task of the day is still not over. For it is necessary 

 to introduce all the observations of the day book, to take out 

 all the results and introduce them into their proper place in 

 the journal of results, or at least into a register of the results 

 of the station, to examine and compare them, in order to 

 see what degree of accuracy has been obtained hitherto, and 

 what is yet needed to complete the work of the station, and 

 to plan accordingly for future observations. It is necessary to 



