372 SCIENTIFIC RECORD FOR 1883. 



sources of error, viz, the assumed regularity of rate of the clock used for 

 observing the transits and the assumed constancy of the azimuth of the 

 hoizontal axis of the instrument in the interval between the transits of 

 the same star east and west. Struve himself discussed these sources of 

 error some years after the publication of his memoir, and was induced 

 to alter his definitive value of the constant aberration to 20" AG'S with 

 probable error of ± 0".017. (It is strange that Strut's first value, 

 20". 445 ± 0".011, has universally been adopted, instead of this corrected 

 value.) M. Nyren also discusses an objection to the methods which 

 have been adopted at Pulkowa for finding the aberration, raised by M. 

 Yvon Villarceau on the grounds that they take no account of the abso- 

 lute motion of the translation of the solar system, pointing out that on 

 any reasonable hypothesis as to the velocity of this motion of transla- 

 tion the effect on the value of the constant of aberration would be prob- 

 ably quite inappreciable in the present state of the art of astronomical 

 observation. 



The observations which form the materials for the determination in 

 the memoir under consideration were made by M. Nyren with the same 

 instrument as that used by Struve, the transit in the i>rime vertical, 

 and reduced and discussed generally in the same manner. The clock 

 used is an excellent one by Dent, and from the attention which has been 

 given to the matter, there is hardly a possibility of error creeping into 

 the result from any error in its assumed rate. With regard to the azi- 

 muth of the horizontal axis of the instrument, two azimuth marks have 

 been set up and frequent determinations of this element made, and 

 every care taken to insure accuracy, so that the present series of 

 observations is probably free from any error arising from this source. 

 The number of stars observed is 24 (comparing favorably with Struve's 

 7), very advantageously situated, having regard to the object in view, 

 and the observations extended from December, 1879, to' January, 1882, 

 thus embracing two maxima and two minima of the aberration for each 

 star. The final value found for the constant of aberration is 



20".517 + 0.20* ± 0".014 



where n is the mean parallax. This latter quantity comes out positive 

 for 10 stars and negative for 14 ; its mean value is 



-f0".002 : ± 0.026 



so that its effect on the deduced constant is quite insignificant. M. 

 Isyren next proceeds to discuss certain observations of arUrsse Minoris, 

 S TJrsvd Minoris, and Oephei 51 Hev., made by M. Wagner during the 

 years 1861-'72. These are observations of transits taken — some by 

 the eye-and-ear method and some by registration on a chronograph — 

 and their discussion gives 20".483 ± 0".012 for the value of the constant 

 of aberration. 



