422 THE POPULAR SCIENCE MONTHLY 



the motion of the earth's pole may be conveniently separated into- two 

 motions, one an annual revolution in a narrow ellipse about thirty feet 

 long and eight feet wide, but varying in form and position, the other a 

 revolution in a circle about twenty-six feet in diameter with a period 

 of 427 days; both motions being counter clockwise. The resultant of 

 these two motions is quite irregular, as may be seen by referring to 

 Fig. 6, which will be explained later. 



From Dr. Chandler's investigations and from the observations for 

 latitude made during the early nineties, it became evident that the 

 movement of the earth's pole was a very complicated one and that an 

 accurate determination of its motion could be obtained only through 

 continuous observations of the latitude at various places on the earth's 

 surface. In 1896 a plan was promulgated by the International Geo- 

 detic Association whereby it was proposed to establish stations for the 

 express purpose of observing the latitude. For reasons to be stated 

 later these observatories were all to be located on the same parallel of 

 latitude and in selecting them, social, hygienic, seism ological and 

 meteorological, as well as mathematical, conditions were considered, the 

 prime requisite being, of course, that all of the stations have a fair 

 proportion of clear nights at all seasons of the year. Seventeen dif- 

 ferent combinations of stations lying between latitudes -+-36° 48' and 

 -f- 44° 50', and including two combinations in the southern hemisphere 

 on parallels — 33° 54' and — 33° 27', were considered. The parallel 

 of -j- 39° 8' was finally chosen with the stations located in Japan, in 

 Italy and the eastern and western parts of the United States. Two 

 other stations were subsequently added, one in Central Asia and the 

 other in the central part of North America, at Cincinnati. 



The preliminary work of establishing the stations occupied about 

 three }^ears and observations were begun at all of them in the fall of 

 1899. The Japanese station is situated very close to the city of 

 Mizusawa (10,000 inhabitants), which lies in a fertile valley 290 miles 

 north of Tokio. The valley is nearly enclosed by two ranges of moun- 

 tains, having a general northerly and southerly direction, the highest 

 peak of which is 6,700 feet above sea-level. The meteorological condi- 

 tions at this station are not especially favorable. There is a large range 

 between summer and winter temperatures and the percentage of cloudi- 

 ness is greater than at any other station. Nevertheless, the two ob- 

 servers, Dr. H. Kimura, director, and Dr. T. Nakano, observer, who 

 have served continuously since the observatory was established, have 

 obtained a most excellent series of results. The number of earth- 

 quakes at Mizusawa is large, but the locality is not affected by these 

 disturbances as much as some other portions of Japan. Since the 

 observatory was established there has been none of sufficient intensity 

 to seriously affect the observations. 



The Central Asian station is located in the Eussian possessions east. 



