MAY 14, 1897.] 



SCIENCE. 



75& 



circle between 1882 and 1891. This series 

 is especially interesting and important in 

 that it covers an interval during which 

 we have very little other information, of an 

 extensive character, as to the variations of 

 latitude. A comparison of the curves of 

 observation and theory thus provided for 

 this decade exhibited a most striking ac- 

 cordance, and seems to leave no possible 

 doubt that Nyren's inference, that his ob- 

 servations do not betray evidence of the ex- 

 istence of the annual component of the polar 

 motion, is erroneous and attributable to il- 

 logical methods in drawing his conclusions. 



THE VAEIATION OF LATITUDE AT NEW YORK, 

 AND A DETERMINATION OP THE CONSTANT 

 OP ABERRATION FROM OBSERVATIONS AT THE 

 OBSERVATORY OP COLUMBIA UNIVERSITY.* 



The results given in this paper were ob- 

 tained from 1,774 observations made be- 

 tween May 6, 1893, and June 20, 1894, with 

 an 8-centimetre "Wannschafif zenith tele- 

 scope. The observations were planned for 

 a determination of the constant of aberra- 

 tion by Kiistner's method. Four groups 

 of stars were used, having mean right as- 

 censions approximately, as follows : 



Group 1 6" 



II 14 



III 18 



IV 22 



Each group contained seven pairs of stars, 

 and covered two hours in right ascension. 

 The groups were observed both morning 

 and evening, whenever the weather per- 

 mitted. The original plan of observations 

 required four observers, but it was unfor- 

 tunately necessary to reject altogether the 

 work of one observer. This caused con- 

 siderable gaps in the series, in addition to 

 those due to unfavorable weather conditions. 



Only observations obtained during the 

 period when it was possible to observe both 



* Abstract of a paper presented by Professor 

 John K. Eees, Professor Harold Jacoby and Dr. Her- 

 man S. Davis. 



evening and morning groups were used in 

 calculating the latitude results employed 

 for the computation of the constant of aber- 

 ration. The observations of each group 

 were gathered together into periods of 

 about ten days each, in such a manner that 

 the weighted mean of the dates should be 

 the same for both the evening and morning 

 groups. In this way the mean latitudes 

 from the two groups should differ only on 

 account of the difference between the decli- 

 nation systems of the two groups, and on ac- 

 count of any error in the assumed value of 

 the aberration constant. They cannot 

 differ on account of variation of latitude, 

 provided any such variation is uniform 

 during the short time of ten days. The 

 result for the aberration constant is there- 

 fore independent of any assumption as to 

 the law of latitude variations. 



The constant of aberration was found to 

 be 20".457 ± 0".013. The mean latitude of 

 the observing station* was 40° 48' 27". 195. 

 The table of definitive latitudes for every 

 ten days showed the variation of latitude, 

 which was very small. The probable error 

 of a single latitude was ± 0".16. 



Observations have been continued from 

 the date last given to the present time by 

 Professor Eees and Dr. Davis, and will be 

 kept up for some time longer. Eeductions 

 of the later series will be finished soon. A 

 series of observations on the same stars has 

 been made and is now being continued at 

 the Eoyal Observatory at Capodimonte, 

 Naples, by Professor Em. Fergola and two 

 assistants, Messrs. Contarino and Angelitti. 



NOTES OF EXPERIMENTS UPON THE RONTGEN 

 RAYS.f 



In most investigations hitherto made 

 for testing the question of the refraction of 



* The observing station was at the new site of the 

 University, about four miles north of the present 

 University Observatory. 



t Abstract of a paper presented by Professor A. W. 

 Wright. 



