ASTRONOMY. 209 



The probable error of a single declination of a comparison star was 

 found to be — 



At Washington ± 0".aU-^ 



At Melbourne rb 0".341> 



AtLeyden ± 0".2o5 



It may be said in passing that the precision of the Leyden results is 

 undoubtedly due to the method of observation (two observers taking 

 l)art in it), and also to the thorough way in which the constants of the 

 Leyden circle were investigated by Kayser. The reduced observations 

 are compared two and two for determinations of the parallax : 



Washington and Melbourne; tt = 8".97 ± 0".03. 



Washington and Sydney ; - = 8".88 ± 0".0o. 



Washington and Cape of Good Hope ; - = 8".90 ± 0".07. 



Melbourne and Leyden ; - = 8".97 ± 0".03- 



Melbourne and Cambridge; - = 9'MJ: -Jo 0".0o. 



In all, these include 70 determinations, and give for the value of -, 

 8".980 ± 0".017. Professor Eastman rejects the Cambridge observations 

 and also certain separate observations; the result from 60 determinations 

 is - = 8".953 ± 0".019, which is adopted. 



Professor Eastman says "the method of determining the solar par- 

 allax from meridian observations of MarSj has never had a fair trial. 

 The principal obsJ;acle to be overcome is the desire of each observatory 

 to co-operate in its own way, if at all, thereby wasting its own work 

 and rendering good observations at other stations useless," and he 

 urges "that at the next favorable opposition of Mars, astronomers may 

 rise above all jealousies and prejudices, and unite upon some plan to 

 give this method one fair trial before it is condemned." The results of 

 Professor Eastman's discussion, and of that of Dr. Winnecke, in 18G2, 

 are in so good agreement that the method certainly deserves, and un- 

 doubtedly will obtain, another trial. 



The next favorable opposition will occur in 1892, and this interval 

 will give all "jealousies" a chance to cool. Mr. Gill has suggested ii 

 reason why the results from Mars observations differ systematically 

 from those by other methods, which is considered by Professor Eastman, 

 on p. 43 of his memoir, and it certainly seems that the experiments of 

 Professor Eastman (which are still in progress) invalidate the proposed 

 explanation. This is a point upon which further light is much needed. 



Transit of Vemts, 1874. — The United States Transit of Venus Commis- 

 sion published a volume containing the chief results of measurements 

 of the photographs of the transit of Venus parties sent out by the 

 United States in 1874. No definitive result for the parallax was given, as 

 some elements for the determination of the final value were still wanting. 

 Professor Tod;l, director of the Amherst College Observatory, has dis- 

 cussed these observations as they stand, and has obtained values for 

 the solar parallax which are probably very near tlie final values. From 

 S. Mis. 109 14 



