TItANSACTIONS OF SECTION E. 717 



shakings accompanying submarine earthquakes, these disturhances resulting in 

 «ffects at least equal to, but probably greater than, those we see produced upon the 

 land. Observations conducted over many years have shown that earthquakes, 

 which are announcements that adjustments in strain or isostasy of rock masses are 

 in progress, are much more frequent along the submerged slopes of the con- 

 tinental plateau than they are on land, which leads to the conclusion that the 

 districts of greatest secular movements on the surface of our planet are to be found 

 beneath the ocean. The best evidence for these facts is furnished by submarine 

 cables. 



Besides interruptions due to waves, the borings of teredo, and other operations 

 in shallow water, we have a class of interruptions at comparatively great depths, 

 in some instances exceeding 2,000 fathoms. In almost all these instances, which 

 •do not occur in the flat plains of ocean beds, but along the edge of submarine 

 banks and the edges of the submerged continental frontier, the cables are 

 apparently buried by the sliding downwards of large bodies of materials from 

 kigher levels. The result of this is that it has often happened that two or three 

 cables, 10 or 15 miles apart, have been destroyed simultaneously. Many examples 

 were given where an earthquake, more or less severe, has been felt on land, and 

 at the same moment a cable has been broken. In some instances when this has 

 •occurred, an impulse has been given which has thrown an ocean like the Pacific 

 iuto a state of agitation for a period of one or two days. 



When these submarine disturbances have been great the resultant earth 

 movement has been such that, with suitable instruments, it might be recorded at 

 any point upon the surface of the globe. 



The most remarkable observations connected with submarine earthquakes are, 

 however, those which have resulted in changes of depth up to at least 200 fathoms 

 over considerable areas. To study these submarine dislocations, and to determine 

 whether cables have been interrupted by artificial operations such as accompany 

 war, or by natural means, horizontal pendulums which will record the unfelt 

 movements of the earth's crust should be established round the shores of all our 

 continents and on oceanic islands. The importance of these observations to our 

 colonies must be apparent. 



Another set of phenomena which promise to throw light upon the fluctuations 

 in the enormous strains within the rocky envelope of our planet, which sometimes 

 culminate in fractures, 100 or more miles in length, are the records of magneto- 

 meters. The effect of torsional and other strains on the magnetic conditions of 

 iron and nickel is well known, and it may reasonably be supposed that kindred 

 eff'ects may be induced by strain in rock-masses. At all events, at three magnetic 

 stations on the coast of Japan, commencing in one case a week, and in another 

 about two weeks, before the great earthquakes of 1896 in that country, the instru- 

 ments showed marked but abnormal movements, these being greatest at the 

 station nearest to the seismic foci. They reached a maximum some hours before 

 the shocks took place, after which unusual displacements ceased. 



Should future observations confirm that which is here noted, we shall then 

 have at our disposal another method of gaining information of changes in opera- 

 tions, the scene of which is hidden from our view not only by the oceans but by 

 the solid rock. 



7. The Congo and the Cape of Good Hope, 1482 to 1488. 

 £y E. G. Ravenstein. 



The discovery of the Congo and of the Cape of Good Hope constitutes two of 

 the most interesting episodes in the history of geographical exploration. Apart 

 from the legends on Behaim's globe, which must be accepted with caution, not a 

 single original report by one of those who took part in these voyages has reached 

 us, and hence the information given even in the best accredited histories of geo- 

 graphical exploration is erroneous in several important particulars. Recently, 

 however, the inscriptions upon some of the columns set up by the early Portuguese 

 navigators have been deciphered ; several ancient manuscript maps have become 



