Gitt— Eruption of Vesuvius and Harthquake at San Francisco. 109 
would produce a volcanic eruption.’ In the ideal case the three 
localities would be expected to be equally distant. It is, however, 
evident that if the displacements were not of equal intensities, the 
distances between the places need not be the same, though, in 
general, we should expect them to be separated by considerable 
intervals. 
That there is a connexion between the frequency of earth- 
quakes and displacements of the poles was called attention to 
twenty years ago by Professor Milne, and has been studied by 
him in detail.* It has been calculated that every great earth- 
quake between 1895 and 1902 caused an average displacement 
of the pole through — 0”:00275.5 The displacement of matter in 
connexion with earthquakes is also a fact recognised by writers on 
this subject.* 
The theory here suggested is that one such displacement, 
whether it be gradual as in the case of an eruption, or more 
sudden as in the case of an earthquake, would be expected to 
give rise to corresponding displacements at other places more or 
less symmetrically situated with reference to the Harth’s axis of 
revolution, producing earthquakes or eruptions as the case might 
be. The following principle on which this view is founded is 
illustrated by the teetotum experiments:—A rotating body, 
containing matter capable of shifting its position, tends to keep 
itself in a state of regular revolution about its axis, owing to the 
way in which the movable matter automatically disposes itself 
with reference to the axis of the body. 
There were certain circumstances connected with the dis- 
turbances which characterised the middle of the month of April, 
1906, which seemed strangely to fit in with the views here 
proposed. 
In the first place the three disturbances took place within the 
space of ten days: Vesuvius very active on April 8th; great 
earthquake in Formosa, April 14th; earthquake at San Francisco, 
April 18th. 
1*¢The Age of the Earth, and other Hssays,’’ by W. J. Sollas, 1905, pp. 84, 86. 
? Bakerian Lecture, 1906. 
3 Kovesligethy. Die Erdbebenwarte, Vol. mr., 1904, pp. 196-202. 
4 British Association, Fifth Report on Seismological Investigation, 1900, p. 109. 
