6g6 THE POPULAR SCIENCE MONTHLY. 



The Challenger left Sheerness December 17, 1872, and crossed the 

 Atlantic four times, making a course of nearly twenty thousand miles 

 during 1873 ; in 1874 she went southward from the Cape of Good 

 Hope, spent nearly a month among the southern ice, dipping into the 

 Antarctic Circle as far as she could with safety, then traversed the 

 seas of Australia and New Zealand, made observations in the Malay 

 Archipelago, and reached Hong-Kong in November, after making a 

 course of more than seventeen thousand miles ; in 1875 she traversed 

 the Pacific, making a course of about twenty thousand miles, and in 

 the early part of 1876 she crossed the Atlantic for the fifth time, to 

 fill up blanks in her former observations, finally reaching England in 

 May. 



During this course of 68,890 miles, 362 stations were established, 

 and observations and collections made at them. The magnitude of 

 the collections is illustrated in a statement made by Professor Alex- 

 ander Agassiz, that, " if a single individual, having the knowledge of 

 eighteen or twenty of the specialists into whose hands they were to 

 be placed, were to work them up, he would most certainly require 

 from seventy to seventy-five years of hard work to bring out the 

 results which the careful study of the different departments ought to 

 yield." They were assigned to various gentlemen recognized as au- 

 thorities in different departments for description group by group. 



The most prominent and remarkable result of the voyage was the 

 final establishment of the fact that the distribution of living beings 

 has no depth-limit, but that animals of all the marine invertebrate 

 classes, and probably others also, exist over the whole of the flora of 

 the ocean. But, although life is thus universally extended, probably 

 the number of species, as of individuals, diminishes after a certain 

 depth is reached. 



Professor Thomson had been led by his researches in the Light- 

 ning to the belief that the chief formation now going on in the bed of 

 the Atlantic was a chalk, " the chalk of the Cretaceous period." This 

 belief grew more firm with continued investigations, but was modified 

 after the Challenger Expedition, when the species deposited were found 

 to be in very few instances identical with those of the chalk, or even 

 with those of the modern tertiaries. " But," he added, in his address 

 on the subject before the British Association, in 1876, " although the 

 species, as we usually regard species, are not identical, the general 

 character of the assemblage of animals is much more nearly allied to 

 the cretaceous than to any recent fauna." 



Professor Thomson had been elected in 1870, previous to the dis- 

 patch of the Challenger Expedition, Professor of Natural History in 

 the University of Edinburgh, succeeding Dr. Allman. He was only 

 relieved from duties during the expedition, and held the professorship 

 until October, 1881, when he resigned it upon a retiring allowance 

 granted him by the Senatus. Immediately on Professor Thomson's 



