ON SEISMOLOGICAL INVESTIGATION. 

 Magxetometee DisTUBBAXCEs — cont'uiued. 



235 



To the above is added 1896, August 27, D, lOh. 54m., H, lOli. Som., 

 ■which agrees with an earthquake recorded in Europe, as, for example, at 

 Catania at 10.52. 



Out of the Utrecht records there are apparently thirteen instances, viz., 

 Nos. 2, 5, 9, 11, 13, U, 15, 18, 19, 20, 21, 22, and 2G, in which the 

 magnetometer perturbations have preceded the records of the seismographs 

 by intervals varying between a few minutes and two hours. 



The disturbances' due to earthquakes are usually easily distinguished 

 from ordinary magnetic disturbances and from those produced artihcially, 

 as for example by the approach and removal of masses of iron. 



A copy of these disturbances was forwarded to Dr. Charles Chree, who 

 very kindly compared the same with his own records obtained at Kew. 

 The results were as follows : — 



Xo. 2. Notbmg special at the times specified. For several days about this date 



innumerable small movements occurred from time to time. 

 „ 5. D, a little movement about 11.25, but not at times stated. H, small 



movement at 10, but various similar movements both before and after. 

 „ 9. D, no movement at 1.42, 1.51, or 1.56. H, a small movement at 1.57. 

 ,, 11. D, nothing at the time stated. H, nothing at 9.51 or 9.58. 

 „ 13. D, numerous very small tremors for some hours before and after time 



stated. H, nothing at 8.20. 

 „ 14. D, nothing at 11.20 or 11.34, or 1.34 A.M. on the 2nd. H, nothing at 



11.36 P.M. on tlie 1st. 

 „ 15. D, curve disturbed this and previous day. Hundreds of movemeirts. 



H „ „ „ ,, 7, :r " 



„ 18. D, nothing at 10.28 specially. Very small tremors 10.25 to 11.30. H, 



nothing at 10.1 ; burr on curve at 10.35. 

 „ 19. D, microscopic tremors about 7.4S and later. H, nothing at 9.0. 

 „ 20. D, considerable magnetic movement 6 to 10 p.m. Nothing special at 



9 P.M. H, ditto. 

 „ 21. D, nothing at 10.27 or 10.43. H, nothing at 10.36 or 10.4.3. 

 „ 22. D, nothing at 11.23 or 11.46 A.M. H, lot of tiny tremors 10 A.M. to 



1 P.M. ; nothing special at 11.26. 

 „ 26. D, nothing at 11.18, 11.29, or 58 ; but at 11.38 somewhat abnormal jerk, 



and small movement at 11.50. H, nothing at 11.29. Movement that 



might well be an earthquake from 11.47 to 12.10. This is certainly 



not a normal magnetic movement. 



Referring to the Utrecht times given for the above thirteen cases. 

 Dr. Chree says that in some cases there was in progress either a moderately 



