172 



Correction of a Marine Barometer for Errors. 



the radius o£ gyration about the centre ; s and k were found 

 from two periods of swing about different axes, and any 



other value of I calculated from I 



s-\-x 



Fig. 3. — Variation of error with position of axis. 

 Fall line is theoretical curve from equation (4). 



Observed values O 



The agreement between observed and calculated values 

 would have been improved by taking into account the slight 

 variations of d with barometric height, which varied slightly 

 during the experiments ; the superior agreement in fig. 2 is 

 due to the introduction of this refinement. 



(7) It appears from this discussion that the adjustment 

 examined above is one which should be made on all marine 

 barometers, whether they are to be used for meteorological 

 ^purposes or for more refined gravity work. Some small 

 alteration in the normal pattern of barometer is probably 

 desirable, because the axis if correctly placed may be found, 

 as in Barometer 1408, to obscure a region of the scale which 



