462 



Commander W. B. Pauli. 



[Feb. 17, 



Summary of the Seismo metrical Observations taken at the Municipal 

 Observatory of Manila, during the various earthquakes ivhich took 

 place from the \4dh to the 25th July, 1880. 



The observations commence by a description of the instruments 

 employed to trace the figures representing the undulations ; Father 

 Faura continues : — " The object of both apparatuses is first to discover 

 the direction of the first horizontal undulation, which is obtained by 

 means of the small ring at the end of the pendulum, and forced along 

 by it. 



" 2nd. To ascertain the general direction of the horizontal undula- 

 tions, and their amplitude by means of the lines which the same 

 pendulum leaves in the powder. 



" 3rd. To obtain the greatest amplitude of the greatest vertical 

 undulation by means of the vertical seismometer. 



"4th. To obtain by a combination of the above results the magni- 

 tude and direction of the oblique undulations. 



" From the indications of these two apparatuses the observations of 

 the terrible phenomena which plunged Manila into the greatest affliction 

 were deduced and given each day. We do not place absolute reliance 

 in them, because the apparatuses can only offer certainty in their in- 

 dications in cases where the complications and violence of the present 

 movements are absent ; but we believe they have a relative and not 

 inconsiderable value, and that they give a sufficiently exact idea of the 

 occurrence, for which we consider them very useful in a comparative 

 point of view, particularly to those who have experienced the terrible 

 phenomena. 



"After these preliminary remarks, we will give the different ob- 

 servations collected each day, which will prove more intelligible by 

 consulting the various figures traced by the pendulum, and these in 

 their turn will prove a complement to those observations. 



" In the months of April and May, commotions began to be felt in 

 the northern provinces of Luzon ; the centre of the seismic oscillation, 

 according to different indications received at this station, seemed to 

 coincide with a volcano extinct for some time, and situated between 

 Lepanto and Abra, in the central range of Luzon, in lat. 16° 22' ~N. 

 and long. 127° E. of the Observatory of San Fernando. 



" In the beginning these disturbances were weak and infrequent ; 

 but in the month of June their intensity sensibly increased, extending 

 to the north and south in a much larger zone. The direction never 

 changed ; and if in some telegrams certain contradictions were ob- 

 served, these appear to have been the effect of the haste with which 

 the observations were taken, which can never be relied on where there 

 are no special instruments used to mark a change in the direction of a 

 seismic oscillation. In the beginning of July shocks were also felt ; but 



