Januabt 2, 1914] 



SCIENCE 



the next hundred years the meridian circle, 

 which is at present the standard instrument 

 for determining the places of the stars, was 

 gradually evolved. In this instrument, a 

 telescope is mounted so that it will point 

 only to stars in the meridian, that is, to 

 stars exactly north or south of the observer. 

 The declinations of stars, corresponding to 

 the latitude of points on the surface of the 

 earth, are then measured by a finely gradu- 

 ated circle. Owing to the motion of the 

 earth all stars cross the meridian twice dur- 

 ing every twenty-four hours. The right 

 ascension, corresponding to longitude, will 

 be given by the time of transit. At first, 

 this time was found by the "eye and ear" 

 method in which the observer counted the 

 ticks of an accurate timepiece and com- 

 pared them mentally with the instant at 

 which the star appeared to cross a wire in 

 the field of view of the telescope. About 

 the middle of the nineteenth century a 

 great advance was made by recording the 

 time electrically on a chronograph. This 

 method was known for many years as the 

 "American "method, owing to its introduc- 

 tion and general adoption in this country. 

 This continued to be the standard method 

 almost to the present time, and an enormous 

 number of observations have been accumu- 

 lated in this way, the total cost amounting 

 to millions of dollars. Perhaps the most 

 valuable work of this kind is that of the 

 Astronomische Gesellschaft, which, by in- 

 ternational cooperation, secured accurate 

 observations of the positions of one hun- 

 dred and sixty-six thousand stars. All 

 stars of the ninth magnitude, and brighter, 

 north of declination — 23° are included. 

 Of the twenty zones, seven were observed 

 in Germany, four in the United States, 

 three in Russia, one each in Algeria, Aus- 

 tria, England, Holland, Norway and 

 Sweden. Of the American zones, one was 

 observed at Albany, one at Washington, 



and two at Cambridge. Each of the latter 

 occupied the time of an observer and sev- 

 eral assistants for twenty years. It was ex- 

 pected that these stars would be re-observed 

 after an interval of about fifty years, to 

 determine the proper motions, or annual 

 changes in position. As the time is ap- 

 proaching when this great work should be 

 undertaken, careful consideration should 

 be given to it. Fortunately, the twentieth 

 century has already developed two new 

 methods which might replace the older 

 plans. The first of these is the transit mi- 

 crometer, in which a motion is given to the 

 wire in the field of the telescope so that it 

 shall follow closely the motion of the image 

 of a star as it transits through the field. 

 A wide difference of opinion exists among 

 leading astronomers as to the best method 

 of securing this motion. In the earlier in- 

 struments constructed by Repsold, the mo- 

 tion was given by a screw turned by the two 

 hands alternately. This method certainly 

 gives excellent results and is still used 

 largely in geodetic work. Any one who 

 has tried it will find that with the rapid 

 motion of an equatorial star under a high 

 power it is difficult to satisfy himself that 

 the wire always bisects the star. If clock- 

 work is used, the rate must vary with the 

 declination and it is strange that this 

 is not done by electrical control, in- 

 stead of the somewhat crude mechanical 

 devices now employed. The wire records 

 its position automatically on a chronograph 

 at short intervals. The plan of permit- 

 ting this record only when the observer is 

 satisfied that coincidence takes place, as is 

 done at Heidelberg, seems a good one. Evi- 

 dently a certain relative motion wiU give 

 better results than a greater or less motion. 

 It would appear to follow logically that this 

 apparent motion should be given to all stars 

 and the record permitted only for the few 

 seconds of apparent coincidence. We can 



