158 Report S.A.A. Advancement of Science. 



object of the latter installation is not simply to make a register of 

 world-shaking earthquakes, but to obtain a continuous record of 

 changes in level. The water of Lake Victoria fluctuates in its height, 

 and it is suspected that this may possibly be due to rock folding. If 

 this is the case, then a seismograph, which can be adjusted to record 

 small changes in level, may possibly yield information connected 

 with the water supply of Egypt. Between Victoria and Cape Town 

 there is a stretch of some 2,000 miles, in which, if two or more 

 stations were established, records would be obtained of immense 

 value to the seismic survey of the world which is now in progress. 



Not only would they be of value as a means of extending our 

 knowledge respecting the nature of the interior of the planet on which 

 we live, but from time to time seismograms would yield information 

 of immediate practical value to South African communities. Certain 

 colonies have established seismographs because they furnish informa- 

 tion as to the cause of a certain class of cable interruption. Cables 

 may cease to work in consequence of the operations of an enemy, in 

 consequence of sub-oceanic seismic disturbances, and for other 

 reasons. A community that can be assured of the reason why its 

 communications with distant places have suddenly ceased, should 

 certainly be less liable to anxiety and alarm than one without similar 

 information. 



For the East Coast of Africa in 12 years I find that out of 19 

 cable interruptions 11 of these have corresponded with unfelt earth- 

 quakes which were recorded at many stations in different parts of 

 the world. 



It cannot be said definitely that these earthquakes were the 

 cause of the interruptions, but the fact that both occurred on the 

 same days, and that it has so frequently happened that cables have 

 been parted by sub-oceanic convulsions, makes it appear likely that in 

 certain instances, at least, we may be dealing with causes and their 

 effects. 



On Jan. 31st of this year an earthquake off the Coast of 

 Columbia, the effects of which found responses in the W. Indies, was 

 responsible for the parting of 8 or 9 cables. 



When one or two more earthquake observing stations have been 

 established in Africa, the origins of these sub-oceanic catastrophes 

 will be localized, and their relationship to the cable interruptions 

 will be better understood. 



Seismographs have been established at Potsdam and at several 

 magnetic observatories in the United States, mainly because the 

 records they yield throw light upon perturbations noted in certaia 

 magnetograms. At other observatories records of unfelt movements 

 of the ground have explained accelerations and retardations in time- 

 keepers, sudden displacements on barograms, and unusual movements 

 of electrometers, the assayers' balance, and other instruments. In 

 addition to changes of level, which are only appreciable after long 

 intervals of time, a horizontal pendulum readily records changes 

 which take place with comparative rapidity. Diurnal changes in 

 level, which are chiefly noticeable in fine weather, have been recorded 



