The clue to the discrepancy is found in Tables XLVI and XLYTT, the values for the 

 differences between individual pendulums and the mean being: 



TABLE XLVI. 



CLristchurch, 1910 



1913 



(mean) 



M,-5. 



M J( -7. 



4586x10 7 sec. 



Hill 

 Kior, 



isc.-j Hi ' see, 



4861 



4856 



:M 



HI HI in ' gee. 



9506 



9460 



More information is obtained by the differences between individual pendulums, 

 which give the values : 



TABLE XLVII. 



Clearly, pendulum No. 5 was reading about 25X10~ 7 sec. too high in 1910, while 

 Nos. 7 and 21 were nearly normal. Equally certainly, no two pendulums were giving 

 consistent readings in 1913, so that the best one can assume is that No. 21 was giving 

 the correct times of swing in that year. 



The cause of these abnormal, but consistent, errors is difficult to trace, and one 

 can only suggest that, in the year 1913, it was associated with the unsatisfactory observa- 

 tions for flexure. Possibly, a change of level took place before the observations com- 

 menced, but no mention has been found in the records of anything bearing on this 

 point. It is possible, but difficult to believe, that a slight earthquake may be the cause 

 of the inconsistencies, and it seems more reasonable to assume that they are due to 

 a faulty setting up of the apparatus. 



The misfortunes of this Expedition at Christchurch are paralleled by those of the 

 previous Scott Expedition, the values for " g " then obtained also varying greatly 

 from one pendulum to another. 



The only safe procedure would be to neglect both sets of observations, but it 

 seems likely that a less inaccurate value for " g " at Christchurch is given by these 

 observations than by those of the <; Discovery " Expedition. This point is discussed 

 later in deriving the most probable values for " g " at the various field stations. 



In these observations, the arrangement which had been designed to take the place 

 of the coincidence apparatus was used for the first time. The arrangement was chosen 



61 



