28 The Period from 1881 to 1890 



V. THE PERIOD FROM 1881 TO 1890 



The advancements of science during this period were of the same gen- 

 eral nature as those in the preceding decade — the completion by observation 

 and experiment of the implications of earlier general theories, such as those 

 of spectrum analysis, uniformitarianism in geology, evolution in biology, the 

 conservation of energy, etc. There were, however, several scientific achieve- 

 ments of the first order of importance, such as Hertz's experimental verifica- 

 tion of Maxwell's electromagnetic theory, the Michelson-Morley ether drift 

 experiment in 1887, Pasteur's conquering of rabies, Koch's work in Berlin, 

 development of aseptic surgery by Lister, discovery of the structure and 

 mode of division of germ cells by Flemming (1882) and Waldeyer (1888), 

 Weismann's theory of heredity through the continuity of the germ-plasm, 

 and the discovery of the existence of vitamins. 



Presidential Addresses 



L. H. Morgan (geology), retiring president at the meeting held in Cin- 

 nati, Ohio, in August, 1881, was unable to deliver an address because of 

 age and infirmities. 



George J. Brush (mineralogy) delivered his address as retiring president 

 of the Association at the meeting held in Montreal, Canada, in August, 1882, 

 on "A Sketch of the Progress of American Mineralogy." (Vol. 31, pp. 

 1-20.) 



J. W. Dawson (geology) delivered his address as retiring president of 

 the Association at the meeting held at Minneapolis, Minn., in August, 1883. 

 The title of the address was "On Some Unsolved Problems in Geology." 

 After sketching the unsolved problems relating to the origin of various 

 series of rocks, he covered similarly the succession of life forms and con- 

 cluded with references to glaciation. (Vol. 32, pp. 1-27.) 



. . . Geology as a science scarcely dates from a century ago. We have reason for 

 surprise in these circumstances, that it has learned so much, but for equal surprise that 

 so many persons appear to think it a complete and full-grown science and that it is 

 entitled to speak with confidence on all the great mysteries of the earth that have been 

 hidden from the generations before us. Such being the newness of man and of his 

 science of the earth, it is not too much to say that humility, hard work in collecting 

 facts, and abstinence from hasty generalization should characterize geologists, at least 

 for a few generations to come. 



Charles A. Young (astronomy) delivered his address as retiring presi- 

 dent of the Association at the meeting held at Philadelphia, Pa., in Septem- 

 ber, 1884, on "Pending Problems in Astronomy." (Vol. 33, pp. 1-27.) 



J. P. Lesley (geology) delivered his address as retiring president at the 

 meeting held at Ann Arbor, Mich., in August, 1885. He gave the address 



