312 



HYDROGRAPHICAL SURVEYING [ch.\p. xiii. 



To calculate the comparison between standard (A) and 

 watch at noon, we have the following comparisons observed : 



Taking any sight, say the middle times at the set we have 

 shown worked out, we find by interpolation that : 



At 3'56 by watch, comparison is 

 At 10-16 „ 



46 

 46 



52-74 



55-07 



and as these are equal times from noon, the noon comparison 

 will be the mean of these, or 46 minutes 53-90 seconds. This 

 differs 0-3 second from the observed noon comparison, which, 

 supposing the comparisons to have been carefully observed, 

 means that there has been a slight irregularity in the motion of 

 the watch, which must be remembered in comparing any 

 meridian distance founded on these sights with others ; but in 

 this case it is so small as scarcely to be taken into considera- 

 tion. 



We now apply this mean comparison of Error of watch : 



Breguet slow 

 Comparison 



Standard A slow on M.T. place 



h. ni. 



4 54 

 46 



10-67 

 53-90 



07 16-77 



We next take the comparisons observed at noon between A 

 and aU the other chronometers ; and, applying them to A's 

 Error, we get the Error of each. 



