ASTRONOMY. 131 



Constant of aberration. — Ilerr Kiistner of tlie Berlin Observatory has 

 made a U«terinination of the constant of aberration with a 4.^ inch 

 broken-back, universal instrument, employing what is commonly known 

 in this country as Talcott's method. His result is a correction of — 0".132 

 to Struve's constant of aberration with the small probable error of 

 ±0",011. A further exhaustive discussion of the observations has led 

 tlic author to conclude that the latitude of his instrument in the spring 

 of 1864 was 0".204±0".02l greater than in the spring of 1885— im- 

 poitant evidence upon the mooted question of the variability of ter- 

 restrial latitudes. 



Professor Hall has recently reduced a series of observations of a 

 LyriQ made with the prime vertical instrument at the XJ. S. Naval Ob- 

 servatory between the years 1862 and 1867. These observations had 

 been designed to give corrections to the a-ssumed values of the constants 

 of nutation and aberration, and an absolute determination of the paral- 

 lax of the star. The series was not continued for a sufficient period for 

 the first purpose, and a preliminary examination having shown that a 

 negative parallax would result, the work has been set aside till the 

 present time. The mean resulting parallax from the 436 observations 

 is ;r=-0".079±0".0134, and the constant of aberration = 20".4506± 

 0".O142. 



On account of the uncertainty in the parallax, Professor Hall has in- 

 troduced a parallax of +0".15, about the mean value indicated by nu- 

 merous observations of this star, and he then obtains a constant of 

 aberration =^20".4542i0".014t. To this result he gives the preference 

 and deduces for the solar parallax 8".810rt0".0062, adopting Hansen's 

 value of the mean anomaly of the earth and eccentricity, Clarke's value 

 for the equatorial radius of the earth, and Michelsou and Newcomb's 

 determination of the velocity of light, 186,325 miles per second. 



Herr jSTyr^u has found in a discussion of the Pulkowa observations 

 of the diflference of right ascension between Polaris and its companion, 

 evidence to confirm the hypothesis, upon which determinations of the 

 aberration constant rest, that the velocity of light is independent of 

 the state whether of motion or rest of the luminous body. 



On the other band the experiments of Michelsou and iVForley seem to 



throw some doubt upon Fresnel's hypotheses that the ether is at rest 



except in transparent media, and that there it participates in the motion 



n' — 1 

 of translation in the ratio — 5—, n being the index of refraction. 



n- ' ° 



Loewy's method of determining the constant of aberration from differ- 

 ential measurements of the changes in the distances of suitably-chosen 

 pairs of stars is to be tested at the Paris Observatory with an equatorial 

 cou<le, and by Professor Oomstock at the Washburn Observatory with 

 suitable apiKiratus fitted to the 6-inch equatorial. The method is essen- 

 tially to bring tlu^ two stars, which may he, say, 00 degrees ajtart in the 

 sky, into the field of an eipiatorial by reflection from the surfaces of a 



