340 HISTOEY OF ASTRONOMY. 



The following are the rules now adopted in the Coast 

 Survey operations for longitude. After the operators 

 have connected the observatories and adjusted their 

 magnets, so that the two stations receive each other's 

 writing well with the least possible pass, the clock of 

 the most eastern station is put on. The observer at the 

 other station then strikes a dot each alternate second, 

 until the observer at the clock station signifies "Aye, 

 aye," by double dots, each alternate second. The ex- 

 change of signals then begins as follows : 



First star. 



Beading of level. 

 Second star. 



Eeversal of instrument. 

 Third star. 



Beading of level, 

 etc. etc. 



In general it is only desirable to observe on the three 

 middle tallies. The observer always informs the re- 

 corder of the tallies observed, and of any lost or badly 

 struck threads. When ten stars have been satisfactorily 

 exchanged, the eastern clock is taken off the circuit, and 

 the western clock put on ; and the exchange of ten stars 

 more completes the telegraphic work for the night. A 

 good determination of the instrumental corrections after 

 the close of telegraph work, is far preferable to any in- 

 crease of the number of star exchanges above twenty. 



When fifty stars .have been satisfactorily exchanged, 

 and on not less than three nights, the observers ex- 



