274 VARIATION OF LATITUDE. 



Ill 1877 Mr. Gr. H. Darwin made a careful and elaborate mathematical 

 discussion of the i^roblera. He showed that in a perfectly rigid globe 

 the jiole could not have wandered more than 3 degrees from its orig- 

 inal position as the result of the continents and oceans changing places. 

 "If, however, the earth is sufficiently plastic to admit of readjustment 

 to new forms of equilibrium, by earthquakes and otherwise, possible 

 changes of 10 or 15 degrees may have occurred. This would require, 

 however, such a complete changing about of the continents and oceans, 

 with maximum elevations and depressions in precisely the most favor- 

 able places, as has certainly never occurred in geologic times." 



The evidence indicates in fact that the, continental areas have always 

 occupied about the same positions as now. 



Thus it would seem that the geologists must abandon the hypothesis 

 of great changes in latitude as a factor in the earth's development, 

 unless a new cause can be found that will move the pole to the extent 

 required by the geologists. 



In an address made before Section A, of the British Association in 

 1892, Professor Shuster stated that he believed the evidence at hand 

 was in favor of the view that there was sufficient matter in interplan- 

 etary space to make it a conductor of electricity. This conductivity, 

 however, must be small, for if it were not, he said, the earth would 

 gradually set itself to revolve about its magnetic poles. However, 

 changes in the x)osition of the magnetic poles would tend to prevent 

 this result. Perhaps the investigator in the near future, working on 

 the suggestion of Dr. Shuster, may find some connection between the 

 earth's magnetism, rotation time, and position of rotation axis. 



The evidence then, at this phase of the discussion, is in favor of the 

 view that there is no adequate reason for believing that any large 

 changes of latitude, amounting to several degrees, have occurred in 

 geologic times. The evidence shows, however, that there are small 

 changes. Are they progressive; does the north pole of tLe earth wan- 

 der slowly but surely farther and farther away from its positions of 

 ages gone by "? 



At the International Geodetic Congress held in 1883 at Eome, Sig. 

 Fergola, of the Royal Observatory, Oappodimonti, IsTaiiles, gave a 

 tabular statement which seemed to show that small but progressive 

 changes had taken place in Europe and America. This table showed, 

 for example, that the latitude of Washington, D. C, had decreased 

 from 1815 to 18G5, 0.47"; at Paris, from 1825 to 1853, the decrease was 

 1.8"; at Milan in sixty years, 1.5"; at Eome during fifty-six years, 

 0.17"; at Naples in fifty-one years, 0.22"; at Konigsberg in twenty- 

 three years, 0.15"; at Greenwich in nineteen years, 0.51". Fergola, at 

 the congress mentioned, suggested a plan for making systematic obser- 

 vations, and he pointed out the favorable location of several observa- 

 tories that were on nearly the same circle of latitude, but differing 

 widely in longitude. Unfortunately this suggestion of Pergola's was 

 not carried out in any way until 1892, when the Columbia College 



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