CHAPTER XIV 

 INCREASING SCIENTIFIC RELATIONS: 1881-1890 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The decade, 1881-1890, was marked by an increase of Gilbert's scientific relations in many 

 directions; he was, so to speak, "discovered" by the scientists of the country during this 

 period, and they were not slow to show their appreciation of his fine qualities. As in the pre- 

 vious decade, he was a frequent speaker at the meetings of the Philosophical Society of Wash- 

 ington, which he served as secretary from 1883 to 1886, as vice president from 1887 to,1891, 

 and as president in 1892, when he delivered a notable address to which reference will be made 

 in the account of that period. The subjects that he presented before this society were as a rule 

 of a general nature; they included a "Graphic table for computation," in 1880; the "Response 

 of terrestrial climate to secular variations of solar radiation," in 1883; the "Diversion of water 

 courses by the rotation of the earth" (mentioned again below); the "Problem of the knight's 

 tour" and a "Concrete problem in hydrostatics," in 1884; "Graphic methods of research" 

 (probably an abstract of his second presidential address before the Society of American Natural- 

 ists as noted below); "Statistics of the society since its foundation" and "Stages of geologic 

 history of the Sierra Nevada," in 1887; and the "Soaring of birds," in 1888. The last subject 

 had very likely been suggested by observations during a voyage across the Atlantic and 

 back in the summer of that year; that his treatment of it was not superficial may be judged 

 from the following extract: 



After a discussion of various qualifying factors, it was stated that when the orbit of the bird [soaring with 

 outstretched wings] is circular, and lies in an inclined plane rising toward the wind, and when the horizontal 

 velocity of the air diminishes uniformly from the highest point to the lowest point of the orbit, the velocity 

 gained by the bird in making the circuit is equivalent to the differential velocity of the highest and lowest layers 

 of air traversed, multiplied by k into the cosine of the angle of inclination of the plane of the orbit. 1 



a review of Whitney's "climatic changes" 



The subjects of two others of the above communications, "Response of terrestrial climate 

 to secular variations of solar radiation" and "Stages of geologic history of the Sierra Nevada," 

 both very briefly abstracted in the society's Bulletin, appear to have been treated more fully 

 in a critical, not to say controversial, review of Whitney's "Climatic changes of later geological 

 times," 2 a review that deserves reading still to-day, as well because of its closely reasoned 

 quality as because of the corrections it provides for certain very questionable conclusions 

 announced in that work. Whitney's leading idea was that a progressive weakening of solar 

 radiation through geological time was responsible for the climatic changes by which former 

 glaciers had been diminished and former lakes had been desiccated. Gilbert took issue with 

 the principle here invoked, and argued that each increment of 4^° C. in mean annual tempera- 

 ture in the past as a result of stronger solar radiation would not only cause increased precipita- 

 tion, but woidd also "double the conjoint power of evaporation and melting to remove precipi- 

 tated snow"; that the glacial period must therefore have had a lower temperature than now; 

 and that the postglacial desiccation of certain lakes in arid interior regions had resulted from a 

 rise, not from a fall of temperature. 



Excessive aridity, therefore, as well as excessive humidity, is caused by solar heat; and every increment 

 of solar radiation tends to magnify the contrast between moist regions and dry regions, making the moist moister 

 and the dry drier. 



1 Science, rii, 1888, 267, 268. 



> Science, i, 1883, 141-142, 169-173, 192-195. 



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