650 



SCIENCE 



[N.S. Vol. XXXVII. No. 956 



A discontinuity at the zenith of about 0".5 is 

 indicated in the Pulkowa Catalogue of 1865, and 

 another of about 0".4 in the Greenwich Catalogue 

 of 1845. 



About half the eircumpolars at Pulkowa cul- 

 minate south of the zenith at their upper transit, 

 and these should give a different latitude from 

 those that culminate north of the zenith at their 

 upper transit, if there is a discontinuity at the 

 zenith. Therefore all the circumpolar observations 

 of the above-mentioned Pulkowa Catalogues were 

 rediseussed to obtain new corrections to the 

 adopted latitude and refraction, introducing into 

 the equations of condition a term (z) to allow for 

 the discontinuity at the zenith. 



In the 1845 catalogue all the 110 eircumpolars 

 were included in the discussion instead of restrict- 

 ing oneself to the 43 used for a similar purpose 

 in the introduction of that catalogue, and in the 

 1865 catalogue all of Gyldfe 's zenith distances 

 were increased 0".15 to correct for the relative 

 personal equation of Gylden and Nyrgn. 



The results of this rediscussion of the Pulkowa 

 observations are as follows: 



Z (Decl. south of zenith relatively too small) 



1845 + 0".09 ± 0".14 



1865 + 0".37 ± 0".10 



1885 + 0".12 ± 0".08 



Refraction 

 fiefraction Constant of 



Constant Catalogue 



1845 57".47 ± 0".064 57".56 



1865 57".45 ± 0".O45 57".56 



1885 57".38 ± 0".035 57".37 



Latitude of 

 Latitude Catalogue 



1845 59° 46' 18".75 ± 0".10 1S".67 



1865 18".67 ± 0".07 18".54 



1885 18".55 ± 0".06 18".54 



These values of the constants of reduction give 

 the following corrections to the published declina- 

 tions : 



Orbit of the Spectroscopic Binary tt' Orionis: 



Olives. J. Lee. 



The variable velocity of the star ir^ Orionis was 

 announced by Frost and Adams with measures of 

 seven three-prism plates in the Astrophysical 

 Journal, 17: 151, 1903. 



The following elements have been derived from 

 these measures and from the writer 's measures on 

 fifty-seven one-prism plates taken with the Bruce 

 spectrograph in the interval 1907-12 : 



Period 3.70045 days 



Eccentricity 0.051 



Longitude of periastron 84° 



Semi-amplitude of oscillation . 58.6 km. 



Velocity of system + 23.7 km. 



a sin i 2,978,000 km. 



Time of periastron passage . . 1907 Dec. 8.83 



or J.D. 2,417,918.83 



The Expression of Pivot Errors hy a Forrmila: 



E. Meldrum Stewakt. 



Even the best measurements of pivot errors of 

 a meridian circle or transit instrument are of 

 course affected by accidental errors, and in the 

 case of fairly good pivots these are no doubt 

 larger than the actual deviations of the pivots 

 from a smooth curve. It then becomes a question 

 what pivot corrections should be adopted both for 

 the positions in which the errors have been ob- 

 served and for intermediate positions. In a recent 

 series of measurements at the Dominion Observa- 

 tory it was foimd that a good representation could 

 be obtained by the use of a Fourier series, and it 

 seems probable that the values so adopted are 

 more accurate than the actual observed values. 



It is evident that a Fourier series can be made 

 to represent the observed values to any required 



