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SCIENCE. 



[N. S. Vol. VIII. No. 204. 



amounts by loug practice. A second of 

 time ill longitude amounts to fifteen hun- 

 dred feet on the map if the place be near 

 tlie equator,, so that, all told, the elimina- 

 tion of personal equation is one of the most 

 important and perplexing problems of prac- 

 tical astronomy. 



The matter became more easily handled 

 on the introduction of the chronograph in 

 1849, for several reasons. In the first 

 place, the Greenwich observers found that 

 by the new method the personal equations 

 were diminished in amount in a general 

 way. Sir George Airy, in his report for 

 1854, sums the matter up in these words : 



"This apparatus, the chronographic, is 

 troublesome in use, consuming much time 

 in the galvanic preparation, the prep- 

 aration of the paper, and the transla- 

 tion of the puncture indications into fig- 

 ures." And in his report for 1855 he also 

 says: "The magnitude of the personal 

 equation in the galvanic-touch method is 

 not above half of that in the eye-and-ear 

 method." But among the observers who 

 use it there is but one opinion on its as- 

 tronomical merits, that in freedom from 

 personal equation and in general accuracy it 

 is very far superior to observations by eye- 

 and-ear method. This judgment of Airy's, 

 however, needs some slight modification, 

 according to the opinions of many of the 

 best practical astronomers now living, and 

 it is worth while to look at the other side 

 in order to see if the eye-and-ear method 

 should be kept up in active practice. First 

 of all, as a method of training young ob- 

 servers it has some importance, as the ap- 

 paratus is greatly simplified if the galvanic 

 connections and preparation are eliminated. 

 It is also often necessary to make time ob- 

 servations at so great a distance from civ- 

 ilization that the delicate chronograph is 

 better left behind. This is a practical dif- 

 ficulty I have often experienced in geo- 

 graphical work in New Mexico and other 



distant portions of the United States ; no 

 chronograph was furnished me, and it was 

 possible to fix the position of a corner post 

 of Wj'oming without a chronograph with 

 an accuracy quite unusual in the U. S. 

 Land Office at that time. Similar consid- 

 erations were of importance in the geo- 

 graphical mapping work of the U. S. en- 

 gineers, where the so-called station error or 

 irregularities in the surface of the geoid 

 far exceeded any errors arising from the 

 use of the eyeand-ear method. After 

 the great Chicago conflagration of 1871 it 

 was a piece of good fortune that I could 

 use the eye-and-ear method, as I was en- 

 gaged in geographical operations for the 

 U. S. engineers, who did not then possess 

 a sufliciently complete supply of chrono- 

 graphs. In 1868 began the observations of 

 the great international star catalogue of the 

 Astrouomische Gesellschaft, which is now 

 approaching completion after thirty years 

 of steady observation. At that time the 

 Council of the Society were undecided as to 

 the use of the chronograph in their cata- 

 logue, and its use or non-use was left to the 

 discretion of the observers. In my own 

 case I decided to begin without one, as the 

 Chicago Observatory, w'here I then was, 

 had not provided money for it, and the 

 chronograph now used by my friend. Pro- 

 fessor Hough, at his new observatory at 

 Evanston, was constructed later. The con- 

 flagration, in its consequences, put an end 

 to my work upon a zone of the A. G. 

 C, and the zone continued at Lund, 

 Sweden, by an appropriation from the 

 Swedish government, and is, I suppose, 

 nearly completed ; but I went far enough, 

 by the eye-and-ear method, to satisfy 

 myself that it would have been entirely 

 practicable to go on and satisfy the re- 

 quirements of the Council as regards ac- 

 curacy. At Harvard College Observatory 

 my lamented friend. Professor W. A. 

 Eogers, used an excellent Bond chrono- 



