418 



Transactions. — CJoemistry and Physics. 



rates a periodic tilting of the pillar, due to the loading of one 

 side or the other by its proper chain and by more or less of it, 

 was obtained bearing some resemblance to a sine curve, and 

 of known period. Owing to an error of cutting the chains 

 they were not of equal weight, one being 17^ lb. and the other 

 211b.,* but as in any case the resemblance to a sine curve 

 was only a rough one, and as also the lighter chain acted 

 upon the pillar at a somewhat greater area than the other, it 

 was not considered worth while to alter it. 



J 



T! 





! r 







t~ - r 



On removing one chain from its box and placing the other in 

 its proper box the total boom-movement was 1"6 mm. I 

 then proceeded to imitate in succession waves of 12 sec, 

 13 sec, Usee, 15 sec, 16 sec, 17 sec, 18 sec, 19 sec, and 

 20 sec. period, whilst the boom period throughout remained 

 as nearly as I could determine at 16 - 5 sec. Before doing so 

 I had increased the speed of the tape to 82 mm. per hour, so 

 that the time-scale might be sufficiently open to enable me to 

 count the individual vibrations of the boom. The various 

 artificial seismograms thus obtained are appended. (Plate L.) 



* I am indebted to the kindness of Messrs. E. Eeece and Sons, of 

 Christchurch, not only for lending me the chains, but for very courteously 

 cuttirjg lengths suitable for the purpose 1 had in view. 



