LONGITUDE OF MOKATTAM. 



271 



The observer at the sending station made contacts at intervals of 15 seconds ; 

 the times not fractional indicate means of times of contacts, a few in each 

 group being usually omitted to make the mean identical with the time of some 

 one particular contact.* The fractional times are the means of the observed 

 times of the corresponding signals at the receiving station, as noted on an 

 ordinary upright galvanometer. The signals were observed at Greenwich by 

 oye and ear in the same manner as at Porfchcurno, the sidereal chronometer 

 in the Computing Koom, sympathetic with the sidereal standard and chrono- 

 graph, being used. 



TABLE III. MEAN ERRORS on GREENWICH MEAN SOLAR TIME, and RATES of the 

 Mean Solar Chronometer C. FRODSHAM 3205, at PORTHCURNO, deduced 

 from the separate Determinations of the preceding Table. 



The errors of the chronometer C. Frodsham 3205 used in Table IV. depend 

 on the fundamental determinations of Table III. 



* It would frequently happen that one or two signals in a group would be lost ; in such cases 

 one or two others would be omitted, as mentioned above, to make the group symmetrical, and so 

 lessen the labour of taking means. 



