THE TWENTIETH CENTURY Up to 1914 travel as developed in the nineteenth century had enabled explorers to reach the poles and cross every great blank in the map of the continents. Tentative experiments had been made with newer methods of transport and investigation but it was only when the war ended and geographers could look about again that the new processes, matured by the intensity of life-or-death experience, became available for the new period which is now with us. Motor engines took the place of steam in the later Norwegian polar expeditions. Shackleton, Scott and Mawson had made attempts to use motor cars and modified aeroplanes in the Antarctic but with no real success and experi ments with radio-telegraphy had tantalized rather than helped some of them. Explorers since 1918 have found to their hand a full equipment for the new era of geographical research. The crossing of the Sahara by a French expedition under G. M. Haardt and L. Audouin-Dubreuil in 1923 proved the power of special types of motor cars to traverse roadless deserts, and the establishment of a trans-desert motor service between Damascus and Baghdad shows that the eastern deserts also can be traversed in this way. Valuable scientific results bearing on the early history of life on the globe were obtained in Mongolia by the expeditions of the Natural History Museum of New York in 1923 and 1924 under R. C. Andrews who-resumed the work in the Gobi desert with the help of motor caravans in 1928.
Frequent flights have shown that no ocean or mountain range interposes a bar to aeroplanes. Alan Cobham in flying from Cairo to Cape Town in 1926 and in encircling Africa in 1928 showed that valuable geographical information could be gleaned from the air in the tropics and Roald Amundsen with Lincoln Ellsworth, an American of means, reached 88° N. in a flying boat in 1925 and returned safely after spending 25 days upon the Arctic ice-floes. In 1926 the American aviator Byrd reached 90° N. in an aeroplane, circled the North Pole and returned without alighting to his base in Spitsbergen. A few days later Amundsen and Ellsworth with the Italian air-pilot Nobile flew in the air-ship "Norge" (which had just flown from Rome to Spitsbergen) to and across the North Pole, landing in Alaska. Nobile's further expedition to the North Pole, which started from Rome with Spitsbergen again as base in May 1928, proved that such attempts are still hazardous. The "Italia" became a wreck in the Arctic and several members of Nobile's party perished.
By means of a number of overlapping photographs taken from a great height a British Air Service company has mapped a large area in Rhodesia and it has been found by the British Ordnance Survey that many features, such as ancient camps and roads, imperceptible on the ground, are clearly visible when viewed from a great height. Photography has also been introduced successfully in surveying from the ground, results of extreme accuracy both for horizontal and vertical angles having been obtained by K. Mason with the photo-theodolite in the Shaks gam valley of the Himalayas in 1926. Other methods have been used with success in the official survey of Canada and in other countries. Radio-telegraphy affords a means of fixing longitudes in any part of the world on land or sea.
Little remains to be done by explorers on land, they must give place there to highly trained surveyors; but even the broad features of the configuration of two-thirds of the surface of the lithosphere are still vaguely guessed at under the veil of the hydro sphere. A British expedition in the "Challenger" broke ground in all the oceans in 1872-76 when about Soo deep soundings were made laboriously with hemp lines several miles in length, each sounding taking a whole working day. In the succeeding decades sounding machines using fine stranded wire enabled the telegraph ships to run many sections across the deepest oceans where sub marine cables were required at the rate of half a dozen soundings per day. During the great war a method of sounding by the echo from the bottom of a noise made at the surface was perfected and in 1926-27 the German research ship "Meteor" under Captain Spiess made an expedition planned by Alfred Mertz in the South Atlantic during which 67,000 separate and almost instantaneous soundings were taken while the ship was under way at intervals of 20 minutes day and night.