334 HYDROGRAPHICAL SURVEYING [chap. xiv. 



where M = meridian distance, 



a = error at place A, before starting, 

 a' = „ A, on returning, 



(i= „ B, 



w=No. of days between first observations at A and 



those at B, 

 m = No. of days between observations at B and those 

 at A, on returning. 



a' - a 

 Then = travelling rate. 



This can be put another way, by example, as follwos : 



Example Let US Suppose we have obtained Error at Maziwi at 



ling Rate, ^^on, August 27 ; we have been to Mesale, and there 



obtained Error at noon on the 31st ; and then, returning 



to Maziwi, have obtained another Error there at midnight 



of September 1-2. 



To find rate in this case we simply divide the difference of 

 the Errors ascertained on the 27th and 1st by 5| (the interval 

 between them). This rate, multiplied by 4 (the interval 

 between sights at Maziwi on 27th and Mesale on 31st), will 

 give the quantity to be applied to the error of the chrono- 

 meter in question at Maziwi on the 27th, to give the error 

 on the 31st on mean time of Maziwi. The difference of this 

 and the error of the same chronometer on mean time of Mesale, 

 as ascertained on that day, will be the meridian distance by 

 that clu-onometer. 

 Form for In working out a meridian distance with several chrono- 

 Distance! ^^ters, it is convenient to use a form, as shown in the example 



of the above-cited instance (p. 336). 

 Rejection Here SO many of the chi'onometers agree closely that the 

 ofResuits. result by D seems doubtful, and looking at the comparisons 

 taken every day with the standard, we see it has been going 

 very irregularly ; we therefore reject it. This should not be 

 done without some independent evidence of this kind ; and in 

 a meridian distance, where the interval of time is great, or 

 where all the chronometers have been going but fairly, as 

 shown by the daily comparisons, it is very unsafe to reject 

 chronometers solely because they vary from a small majority 

 of the others. 



