FIFTY YEARS' PROGRESS IN SCIENCE. 467 



their scientific investigations into the Pamir and Eastern Turkestan, until at last 

 the British and Russian surveys have been connected." 



Again, fifty years ago the vast Central Regions of Africa were almost a blank 

 upon our best maps. The rudely drawn lakes and rivers in maps of a more an- 

 cient date had become discredited. They did not agree among themselves, the 

 evidence upon which they were laid down could not be found, they were in many 

 respects highly improbable, and they seemed inconsistent with what had then 

 been ascertained concerning the Niger and the Blue and White Niles. At the 

 date of which I speak, the Sahara had been crossed by English travelers from 

 the shore of the Mediterranean, but the southern desert still formed a bar to 

 travelers from the Cape, while the accounts of traders and others who alone had 

 entered the country from the eastern and western coasts were considered to form 

 an insufficient basis for a map. 



Since that time the successful crossing of the Kalahari desert to Lake Ngami 

 has been the prelude to an era of African discovery. Livingstone explored the 

 basin of the Zambesi, and discovered vast lakes and waters which have proved to 

 be those of the higher Congo. Burton and Speke opened the way from the west 

 Coast, which Speke and Grant pursued into and down the Nile, and Stanley 

 down the course of the middle and lower Congo; and the vast extension of Egyp- 

 tian dominion has brought a huge slice of equatorial Africa within the limits of 

 serai-civilization. The western side of Africa has been attacked at many points. 

 Alexander and Galton were among the first to make known to us its western 

 tropical regions immediately to the north of the Cape Colony ; the Ogowe has been 

 explored ; the Congo promises to become a center of trade, and the navigable 

 portions of the Niger, the Gambia, and the Senegal are familiarl)'' known. 



The progress of discovery in Australia has been as remarkable as that in 

 Africa. The interior of this great continent was absolutely unknown to us fifty 

 years ago, but is now crossed through its center by the electric telegraph, and no 

 inconsiderable portion of it is turned into sheep-farms. 



[ To be Continued ] 



An eminent scientist says that all chemical actions may be- regarded as ac- 

 tions either of contact or mixture, and are regulated in the former case by speci- 

 fic gravity and molecular weight — in a word, by the molecular volume of the 

 bodies present, and in the second case by their molecular weight. In the gener- 

 al hypothesis of chemical action which he advances he rejects entirely the usually 

 accepted notions of molecule and atom, and substitutes what are conveyed by 

 the terms equivalent and atomic volume. 



