564 



SCIENCE. 



[N. S. Vol. I. No. 21. 



Shuster stated that he believed the evidence 

 at hand was in favor of the view that there 

 was sufficient matter in interplanetary space 

 to make it a conductor of electricity. This 

 conductivity, however, must be small, for if 

 it were not, he said, the earth would gi-adu- 

 ally set itself to revolve about its magnetic 

 poles. However, changes in the position 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 be- 

 tween 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 sev- 

 eral degrees, have occurred in geologic 

 times. The evidence shows, however, that 

 there are small changes. Are they progres- 

 dve; does the north pole of the earth wan- 

 der slowly but surely further and further 

 away from its positions of ages gone by? 



At the International Geodetic Congress 

 held in 1883 at Rome, Sig. Fergola, of the 

 Royal Observatory Cappodimonti, Naples, 

 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 1845 

 to 1865, 0.47" ; at Paris, from 1825 to 1853, 

 the decrease was 1.8" ; at Milan in 60 years, 

 1.5" ; at Rome diiring 56 years, 0.17"; at 

 Naples in 51 years, 0.22"; at Konigsberg in 

 23 years, 0.15"; at Greenwich in 19 years, 

 0.51". Fergola, at the Congress mentioned, 

 suggested a plan for making systematic ob- 

 servations, and he pointed out the favora- 

 ble location of several observatories that 

 were on nearly the same circle of latitude, 

 but differing widely in longitude. Unfor- 

 tunately this suggestion of Fergola's was 

 not carried out in any way until 1892, when 

 the Columbia College Observatory arranged 



to work in conjunction with the Naples Ob- 

 servatory on the problem. This series of 

 observations was begun in the spring oT 

 1893, and will be continued several yeai*s. 



The data given by Fergola at Rome in 

 1883 showed a diminution of latitude in 

 every case ; other data showed a similar 

 diminution ; however there were excep- 

 tions, where the latitudes seemed to in- 

 crease. 



The investigations that have been going 

 on since 1883 throw doubt on the progressive 

 changes in latitude, or at least such changes 

 are masked by proved periodic changes. 



For a long time, since 1765, periodic 

 changes have been looked for, because the 

 theory of a rotating earth, an earth hav- 

 ing the form of a sphere flattened at the 

 poles, or, more accurately, an ellipsoid of 

 revolution, demanded such changes ; but 

 the theory did not furnish any clue to the 

 amount of changes, except that they must 

 be very small. This theory shows that if 

 the earth was absolutely rigid and revolved 

 about its shortest axis (called the axis of 

 figure) at any time it would continue to 

 revolve about such axis forever, unless dis- 

 turbed by some outside force. If so dis- 

 turbed, then the axis of rotation would no 

 longer coincide with the axis of figure — the 

 axis of rotation would intersect the earth's 

 surface at points away from the points 

 where the axis of figure comes out. But 

 the theory also showed that the new axis 

 of rotation would revolve about the old one 

 in a period of 304.8 days. This period 

 comes from the knowledge of the magni- 

 tude of precession and nutation, and is 

 known veiy accurately. 



We would expect therefore that changes 

 in latitude would show this 305-day period. 



Several attempts have been made to de- 

 termine the distance between the two axes 

 (figure and rotation axis) from changes in 

 latitudes. 



The celebrated astronomer Bessel made 



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