Maech 23, 1906.] 



SCIENCE. 



451 



tenth or eleventh magnitude may be re- 

 corded, and a large part of the entire re- 

 gion may be photographed in a single 

 night. It might be better to photograph 

 a zone a little north of the equator in mid- 

 winter, at a station so far north that ob- 

 servations could be made continuously dur- 

 ing twenty-four hours. Many forms of 

 small systematic error would thus be elim- 

 inated. 



The Polaris Vertical Circle Method of De- 

 termining Time and Azimuth: F. H. 

 Seares. 



The vertical circle method of observing 

 for time and azimuth has been known for 

 a century or more, is capable of affording 

 very precise results, but has never found 

 general acceptance on account of a lack of 

 satisfactory methods of reduction. The 

 most important methods have been devised 

 by DoUen and Harzer. The formulae of 

 DoUen are not sufficiently accurate for 

 many purposes ; moreover, the Ephemerides 

 necessary for the use of his formulse are 

 no longer published. The method of re- 

 duction proposed by Harzer lacks nothing 

 in precision, but the calculations are un- 

 necessarily long. Laws Observatory Bul- 

 letin No. 5 contains a method which affords 

 the desired precision, and permits of a 

 saving of three tenths in the labor of cal- 

 culation as compared with the process of 

 Harzer. The present paper separates the 

 features which are essential for the prac- 

 tical application of the method from cer- 

 tain purely theoretical considerations con- 

 tained in Bulletin No. 5, and is intended 

 to exhibit more clearly the simplicity and 

 brevity of the operations involved in the 

 employment of the writer's formula. 



Although it is not contended that the 

 vertical circle method can profitably re- 

 place the older methods in all cases, the 

 following advantages are claimed: 



1. A saving in labor when it is necessary 

 to determine both time and azimuth. 



2. A gain in precision and a saving in 

 labor in the determination of time with 

 unstable instruments, especially when it is 

 desirable to secure all possible accuracy. 



3. A frequent saving in time and labor, 

 irrespective of whether the instrument be 

 stable or unstable, when it is necessary to 

 work through clouds. 



4. When applied to the engineer's tran- 

 sit, it affords a very simple and precise 

 method of determining time in the field, 

 and frees the observer from any necessity 

 of waiting for an elongation of Polaris in 

 order to secure observations for azimuth. 



Determination of Adjustment Errors for 

 the Polar Axis of an Equatorial: Eric 



DOOLITTLE. 



The method consists in measuring the 

 position angle of a pair of stars close to the 

 pole. Each measure gives an equation for 

 determining the position angle, supposed 

 unknown, and the instrumental errors. 

 From several measures at different hour 

 angles the latter can be determined with a 

 degree of accuracy probably higher than 

 by any method in which the circles of the 

 instrument are used. The ordinary for- 

 mula must, however, be considerably modi- 

 fied for this purpose. 



Two determinations of the error of ad- 

 justment for the 18-inch equatorial belong- 

 ing to the Flower Observatory were made, 

 the results agreeing within 1 second, and 

 the probable error of each result being less 

 than 1.5 seconds. 



The advantages of the method are that 

 observations are very easily made, that 

 there is no moving of the dome or observing 

 chair, and that the time need only be known 

 very roughly. The setting circles are not 

 read, and hence their errors of graduation 

 do not affect the result. The disadvantage 

 is that the subsequent labor of reducing 



