672 GEOGRAPHY 



Such also are the distribution of land and water, the configuration 

 of the continents, their streams and mountains, their valleys and 

 plains, which have changed but little in historical times; but fa- 

 miliarity with these features tends to forgetfulness of the fact that, 

 like actors on a stage, their appearance in the theatre of history has 

 been gradual, and that, though their actual positions have remained 

 unchanged, their relative positions have varied through the ages, 

 and moreover that they are often destined to play more parts than 

 one. 



A sea like the Mediterranean may at one time be the centre of 

 commercial activity, and then become a backwater, while commerce 

 streams along an ocean route round Africa. A few centuries pass, 

 and the cutting of the Suez Canal, coupled with the development 

 of steam navigation, restores it to its ancient and honorable estate 

 as a highway of communication with the East, and the great cities 

 on its shores, like Venice and Genoa, after a long period of decay, 

 begin to resume their pristine vigor. 



Since long before the beginning of human life, stores of gold and 

 coal and other minerals have lain in the bosom of the earth; but 

 their development as the sites of great centres of population has in 

 most cases been essentially linked with the element of time. The 

 rapid growth of Johannesburg into the position of the largest city of 

 South Africa w r ould have been as impossible without the recent dis- 

 covery of the cyanide process, as was the development of the great 

 coal-fields -- the most striking factor in the shifting of great masses 

 of population in modern times - - until the invention of the applica- 

 tion of steam power to machinery. 



The great forces of nature show little tendency to change and may 

 be usefully applied to the elucidation of many geographical problems, 

 as for example in the case of the early voyages round the Cape of 

 Good Hope. Bartholomew Dias, the first discoverer of the cape, 

 encountering adverse westerly winds on his return voyage, must as 

 assuredly have been there in our northern summer months, when the 

 shifting of the trade- wind system brings the cape into the influence of 

 the westerly winds, as was Vasco da Gama there in our winter months, 

 when easterly gales prevail. Similarly the voyage of Odysseus may be 

 largely elucidated with the help of a modern manual of sailing direc- 

 tions for the Mediterranean. But it is into the fluctuating fortunes 

 of individual districts that the time-factor chiefly enters and demands 

 a nice discrimination between the meaning of actual and relative 

 geographical position. 



Potentiality precedes performance. An island may be long the 

 home of a hardy race of mariners before a field adequate to the display 

 of their abilities is unveiled. The site of a great city may seem to have 

 been predestined for centuries, before the opportunity for its develop- 



