ON SEISMOLOGICAL INVESTIGATIOX. 181 



and the pendulum travels eastwards, whilst at night moisture is accumu- 

 lated, and it sinks.' 



VIII. The Perry Tromometer. By John Milne, F.R.S., F.G.S. 



A Perry Tromometer, similar to that described in the Report of this 

 Committee for 1896, with photographic recording apparatus, has been 

 constructed, and for some days installed at Shide. Its sensitiveness to 

 elastic tremors was such tiiat it recorded trains moving at a distance of 

 over half a mile, carriages at a distance of a quarter of a mile, and all 

 v-ehicles passing along a road near to the building in which it was placed. 

 For these reasons it was dismantled, but it may be again used when a site 

 free from the above-mentioned artificial disturbances, to which may be 

 added the sound-waves from heavy guns fired at a distance of five or six 

 miles, can be found. 



In conclusion to the preceding sections of the Report the fact that the 

 records of earthquakes and other movements have been continuous has 

 been in consequence of the great interest taken in the observations by my 

 assistant, Shinobu Hirota, who not only understands the working of the 

 instruments in all their details, but has from time to time shown con- 

 siderable ingenuity in devising and constructing new pieces of apparatus. 



IX. fSuh-oceanic Changes. By JoiiN Milne, F.R.S., F.G.S. 



The object of the following notes, which are an epitome of a paper to 

 be communicated to the Royal Geographical Society of London, is to show 

 that beneath seas and oceans there are a certain class of geological changes 

 in operation Avhich are more frequent, and often more intense, than 

 corresponding changes on land. 



The sites of these changes are to be found below low-water mark at 

 comparatively shallow depths on submerged plateaus surrounding conti- 

 nents and islands, and on the face, and especially near to the base of the 

 steeper slopes of continental domes, and around submarine banks at 

 depths which may even reach 4,000 fathoms. On the level floor of 

 oceans, where sediments accumulate with immeasurable slov/ness, and 

 whei-e for years and years ocean cables lie undisturbed, geological changes 

 are, so far as a lifetime is concerned, not recognisable. 



The submarine operations to which it is particularly desired to draw 

 attention are those which are seismic and volcanic, the former at least 

 often being accompanied by the displacement as a landslide of such 

 enormous volumes of material that the whole surface of an ocean may be 

 agitated. Evidences that such displacements have had a reality is to be 

 found in the conditions under which cables have been buried, and in the 

 marked change in soundings near to spots where seismic efforts have been 

 exerted. 



Other causes leading to displacement of materials on the face and 

 near to the base of submerged slopes are overloading by sedimentation, 

 erosion, the escape of water from submarine springs, and the effects of 

 currents. 



The various sub-oceanic phenomena to which it is particularly desired 

 to call attention will be treated in the following order : — 



1. Brady seismic action. — Because earthquakes originating beneath 



' British Association Beport, 1895, pp. 133-139, 



