AT KEW OBSERVATORY AND THEIR DISCUSSION, 



469 



TABLE XXIV. True Secular Change of Zero, error in inches. 



A horizontal line indicates the break down and repair of the instrument ; readings above and below 



it are not comparable. 



The changes were certainly in a good many instances discontinuous. Thus aneroid 

 No. 1 experienced at least 9 sudden changes of reading of "1 inch or more, 3 of 

 these being rises and 6 falls. No. 2 had only one sudden change so large as this. 

 It occurred in May, 1895, and amounted to + '18 inch. No. 3 had two sudden falls 

 of appreciable magnitude, both in June, 1895. No. 7 had two sudden changes 

 exceeding '1 inch, one a rise, the other a fall. In the case of Nos. 4 and 8, except 

 on the occasion of the former breaking down, there was no sudden change as large as 

 1 inch. The constancy of zero in the former aneroid was especially notable, because 

 it experienced more variations of pressure than any of the others. The cause of the 



