CHAP. XIV.] TELEGRAPHIC MERIDIAN DISTANCE 333 



in pairs in such a manner that it shall produce little or 

 no effect on the result, which is a desirable object to 

 attain. 



In order to secure reliable results, the observations should Return 

 extend over two or more days, exchanging signals at noon and £)e*taii°^of 

 midnight on each consecutive day. The error of the chrono- Tele- 

 meter being obtained at regular intervals, a satisfactory check Meridian 

 is thus afforded on the observations themselves, and also on the Distance 

 regularity of the rate of the chronometers tliroughout the 

 whole period. The observers should then change ends and 

 repeat the series. A full report of the operations should be 

 rendered, giving details of the observations for time, the 

 various comparisons between the chronometers used for send- 

 ing and receiving signals, and the standard clironometer used 

 at each end for carrying on the time. When it is impracticable 

 for the observers to change ends, the results of any previous 

 observations that may be available for determination of 

 personal equation should also be included. For the form in 

 which these details may conveniently be rendered, reference 

 should be made to the various pamphlets that have been issued 

 from time to time by the Hydrographical Department, giving 

 the results of such observations. 



CHRONOMETRIC MERIDIAN DISTANCES. 



When we have no telegraph, we must have recourse to 

 chronometers for conveying the time. 



Having obtained sights at the two places whose meridian 

 distance we require, we come to the consideration of the rate 

 to be used. 



If we have been able to run backwards and forwards, as 

 recommended on p. 294, we shall use a traveUing rate. 



The algebraic formula for finding the meridian distance by Formula 

 travelling rate, when we return at once to the original station, l^^^^gj. 

 is as follows ; ^^^S Rate 



a' -a 



M^Q-a-n . 



m + n 



