LONGITUDE OF MOKATTAM. 



275 



In the make and break method the circuit was completed and broken at 

 the sending station at intervals of 15 seconds, the operator using alternately 

 the positive and negative key. At the receiving station the first start of the 

 beam of light was the phase of signal observed. The signals referring to 

 completion of the circuit are collected into one group, without distinction of 

 quality, positive or negative ; and those referring to break of the circuit into 



N N 



