264 POPULAR LECTURES AND ADDRESSES. 



paper by Dr. Nyscn, of Pulkova Observatory, in 

 which a similar negative conclusion as to con- 

 stancy of magnitude or direction in the deviation 

 sought for is arrived at from several series of the 

 Pulkova observations between the years 1842 and 

 1872, and containing the following statement of his 

 conclusions } : 



" The investigation of the ten-month period ot 

 latitude from the Washington prime vertical 

 observations from 1862 to 1867 is completed, 

 indicating a coefficient too small to be measured 

 with certainty. The declinations with this instru- 

 ment are subject to an annual period which made 

 it necessary to discuss those of each month separ- 

 ately. As the scries extended through a full five 

 years, each month thus fell on five nearly equi- 

 distant points of the period. If x and y represent 

 tlie coordinates of the axis of instantaneous rota- 

 lion on June 30, 1864, then the observations of the 

 separate months give the following values of * 

 and y : 



.' [!'< r latrr investigations by Ncwcomb and others on this sub- 

 Irom my 1'irsMrnli.il Addresses of 1891 and 1892 to 

 tin- R'.yal Society. K., March 22, 1893.] 



