128 F. OMORi : 



Secondly, the complete periods of vibration of the EW and 

 NS component horizontal pendulums are at present, for a special 

 purpose, set unequal to each other, being respectively 28 and 17 

 seconds. The period of each pendulum can be raised much above 

 these values, but it was found convenient not to make it much 

 above 30 seconds, in order to prevent the pendulums assuming too 

 great deviations in their daily oscillations and other slow 

 movements. 



III. 



9. PI. Ill illustrates the portable form of my Horizontal 

 Pendulum, recently set up in the Seismological Institute, fig. 6 

 and fig. 7 giving its front and side elevations. 



The heavy-bob of the pendulum is a thin brass cylinder, a, 

 filled with lead, 6^ cm. in diameter, 9 cm. in height and about 3 

 kgm. in weight, attached at a little above its centre of gravity 

 to a strut, b, which is an iron rod, 8 mm. in diameter, furnished 

 at the end with a sharp conical point. The strut is pivoted in a 

 conical steel socket, c, fixed to the base of a strong cast iron 

 stand, d, which is bolted to a foundation column, and from whose 

 top the pendulum is hung by means of a fine wire, e. The 

 vertical distance between the points of support and suspension is 

 1 m., and the horizontal distance between the point of support and 

 the axis of the heavy cylinder 75 cm. The loAver end of the 

 wire, e, is attached to the cylinder in a manner similar to that 

 in the case of the instrument described in the preceding section. 



10. Fig. 8 shows in section and plan the details of the 

 mechanism applied to the top of the cast iron stand, by means of 

 which the necessary adjustments can be effected. 



