Klotz. — Transpacific Lonyifndes. 59 



cable-siphon. In receiving signals there is, of course, only the 

 record of the cable- siphon, the other siphon recording only the 

 chronometer-beats, which, on the fillet, measure about 1 in. for 

 the two seconds. The speed of the fillet may be varied to any 

 degree. It will be seen that a comparison of clocks by this 

 means is simply a matter of careful linear measurement. Were 

 the records at the two stations instantaneous, then the two- 

 records would be identical ; but such is not the case. Each 

 signal arrives late at the distant station, and therefore the two 

 records will differ by twice the time of transmission, assuming 

 that the time of transmission is the same in each direction, an 

 assumption which we caiinot avoid. On the long section of the 

 cable between Bamfield and Fanning, about four thousand two 

 hundred statute miles, the time of transmission was a third of 

 a second, equivalent to about twelve thousand statute miles 

 per second. 



In the first longitude -work by cable before the introduction 

 of the recording- siphon, instead of arbitrary signals, the clock- 

 beats were sent by hand at intervals generally of ten seconds,, 

 and the time of arrival of the signal, as indicated by the reflecting- 

 galvanometer, was noted by the " eye and ear " method. The 

 uncertainties and " personal equation " in this method of ex- 

 change and comparison of clocks are apparent. 



We have now explained briefly how the clock- correction is 

 obtained for a given instant, and how the comparison of the 

 two clocks is made. The application of the clock-corrections 

 respectively to the times of exchange gives apparently the local 

 sidereal time for each place at the same instant. Each value is, 

 however, affected by a small correction — the personal equation 

 of each observer. As the quantity sought is the difference be- 

 tween the local sidereal times, the absolute personal equation 

 of each observer is unimportant : it is the difference between the 

 two personal equations that affects the difference of longitude. 

 On land lines, where the ready means of transportation is good,, 

 it has been customary (up to the present, when, by the intro- 

 duction of the registering-micrometer, the personal equation is 

 eliminated) for the observers to exchange stations, the mean 

 result of the two differences of longitude being free from personal 

 equation : this is on the assumption that the personal equation 

 of the observers remains constant during the longitude campaign. 

 On this assumption, if there is a series of stations odd in number, 

 and the observers occupy -alternate stations, it will be seen that 

 the odd-numbered stations ^vill be free from personal equation, 

 and the even-numbered ones affected by it. Now, between 

 British Columbia and Australia, and also between British 

 Columbia and New Zealand, the number of stations is odd — 

 i.e., there are three intermediate stations, Fanning, Suva, and 



