November 25, 1898.] 



SCIENCE. 



7-21 



the new point of view with a mind as free 

 as possible from prejudice, and with a 

 single eye to the truth. In short, the ideal 

 investigator is the scientific independent, 

 ^ the chemical 'mugwump.' It is too un- 

 reasonable to hope that the problems of the 

 twentieth century will be dealt with in this 

 thoughtful but untrammeled fashion ? 



We Americans rejoice in having on our 

 side of the ocean the world- renowned names 

 of several great men, of Wolcott and Wil- 

 lard Gibbs, of James Crafts, Edward Mor- 

 ley, the late Josiah Parsons Cooke and 

 others, who have combined chemistry with 

 physics and mathematics ; but, nevertheless, 

 one must admit that America has not done 

 .>j as much as one could wish toward building 

 up the fabric of modern physical chemistry. 

 Although science is world- wide, and scien- 

 tific men should be cosmopolitan, the ex- 

 istence of this Association proves that there 

 is a patriotic side to the matter too. "While 

 welcoming the truth, wherever it is discov- 

 ered, let us then do all we can to further its 

 emanation from American laboratories and 

 writing desks. 



Theodore W. Kichaeds. 



Haevaed University. 



A CENTURY OF PERSONAL EQUATIONS.''' 



In 1795 Maskelyne, Astronomer Koyal at 

 Greenwich, discovered that his assistant, 

 Kinnebrook, was in the habit of noting star 

 transits about seven-tenths of a second of 

 time later than himself, and discharged the 

 poor fellow as ' vitious ' in his method of 

 observing. The matter attracted little at- 

 tention until, about twenty-five years later, 

 the celebrated Bessel investigated it, and 

 showed that the best observers whom he 

 could influence exhibited similar discrep- 

 ancies in their transits. Bessel himself 

 was exceptionally early in his times, and 

 found that other astronomers were usually 



* See also my article in Science for Nov. 26, 1897. 



later. The theory which he formed was 

 that the early observers, Maskelyne and 

 Bessel himself, heard their clock beats be- 

 fore they saw the stars' images, while the 

 late observers, Kinnebrook, Argelander, 

 W. Struve and others, saw first and then 

 heard. The theory of Bessel has been gen- 

 erally adopted by astronomers and psychol- 

 ogists, and the investigation of the differ- 

 ences between astronomers has been pursued 

 pretty continuously since 1836, when Airy, 

 as Astronomer Royal at Greenwich, began 

 a regular continuance of Bessel's investiga- 

 tion soon after entering upon that office. 

 The matter was more or less perplexing to 

 the Greenwich observers for the twenty 

 years between 1836 and 1855. In 1853 

 the so-called eye-and-ear method, which 

 had been employed for about a century 

 previously, was laid aside at Greenwich for 

 most purposes, and replaced by the Amer- 

 ican, or chronographic, method of galvanic 

 registration, invented by Sears Cook Walker 

 in 1849. 



During the first half of the century, 1795 

 to 1895, to which this paper refers, obser- 

 vations of transits were made by Bradley's 

 method, or by eye and ear, but for the sec- 

 ond half century observers have had the 

 benefit of AValker's invention, and of the 

 ingenious apparatus constructed bj' the 

 Bonds and other mechanicians for the pur- 

 pose of carrying out the principle intro- 

 duced by Walker. The investigations of 

 personal equation up to 1853 are based, 

 then, upon experimental psychology as 

 developed by Bessel, and have led to a 

 pretty complete body of empirical facts in 

 that direction. But Bessel and his asso- 

 ciates considered the whole matter enigmat- 

 ical and difficult to trace, owing to the fact 

 that the phenomena are subconscious and 

 not easy to bring under the laws of experi- 

 mental science. Observers noted large 

 differences in their times, a second or more 

 and could not reduce them to moderate 



