1881.] Notes on the Earthquakes of July, 1880, at Manila. 465 



we continued to be under the influence of the phenomenon. In this 

 first repetition the oscillation and trepidation movements only were 

 experienced, but with extraordinary violence. The oscillation of the 

 pendulum was directed from S.E. 15° E. to KW. 15° W. The ampli- 

 tude described an arc of 12° 30', but with the following peculiarity, 

 that this did not consist of a perfect oscillation, but of three semi- 

 oscillations, which show plainly the violence of the shocks (see in 

 fig. 3 the lines marked with the letters aa r , bb', rr"). The pendulum in 



Fig. 3. 



the first impulse from south-east to north-west reached the altitude 

 indicated by the line aa' ; on returning to its point of departure it 

 received a new impulse which not only destroyed the velocity which 

 it had acquired in its descent, but obliged it to ascend a second and 

 third time almost to the same height it had attained by its first 

 impulse. 



" It is true that the inclination of the buildings was not equal to 

 the deviation of the pendulum, but who is competent to understand 

 the terrible convulsions which the former underwent during such 

 repeated and violent shocks ? The three above-mentioned convulsions, 

 joined to the vertical undulation which reached 24 millims., being taken 

 into account, the only thing to be astonished at is, that many more 

 buildings were not thrown down. The pendulum continued oscillating 

 during the whole of the evening from north-east to south-west. 



