October 7, 1904.] 



SCIENCE. 



467 



field parties courtesies and. assistance without 

 wMch the execution of the work would have 

 been impracticable. This was specially the 

 case at Guam and Midway Islands, where the 

 parties were almost wholly dependent upon the 

 cable staffs. The transportation to and from 

 these islands is very infrequent and was the 

 cause of the long delay in the completion of 

 the field work. 



In the determination of time at the several 

 stations the method set forth in Appendix 7, 

 of the ' Coast and Geodetic Survey Eeport,' 

 for 1898 was carried out except that it was 

 impossible to observe the same stars at both 

 stations involved in each determination of a 

 difference of longitude, on account of the great 

 difference of longitude and also the unfavor- 

 able weather conditions which often neces- 

 sitated the observation of different stars on 

 consecutive nights. The stars were selected 

 almost exclusively from the list given in the 

 Berlin Jahrhuch, and it is believed that the 

 results must be very little if any in error on 

 account of errors of the right ascensions. 



The greatest difficulty to be overcome was 

 the eliminations of the difference of personal 

 equation of the observers. 



Since 1891, the Germans have used the 

 Eepsold registering micrometer on their tran- 

 sits and their experienced observers seem to 

 have almost no personal equation in its use for 

 the determination of time. 



In eight differences of longitude determined 

 by them, 1893 to 1903, an exchange of instru- 

 ments and observers took place midway in the 

 work of each determination, thus giving a 

 determination of the sum of the differences of 

 instrumental and personal equations. 



The following results are taken from the 

 Astronomisch-Geodatische Arbeiten of the 

 Preussischen Geodatischen Institutes for 1902 

 and 1904. 



TJbagsberg-Gottlngen 



Ubagsberg-Bonn 



Bonn-Gottingen 



1893 s 



III. Borrass— II. Albrecht —0.009 



" —0.019 



" " — 0.034 



1898 



Knivsberg-Kopenhagen III. Albrecht- II. Schumann— 0.034 



Knivsberg-Kiel " " — 0.033 



1900 



Fotsdam-Burkaiest III. Albrecht— II. Borrass — 0.017 



1901 



Potsdam-Pulkowa III. Albrecht— II. Borrass — 0.025 



1903 

 Potsdam-Greenwich III. Albrecht— II. Wanach 0.000 



Had no exchange of place of instruments 

 and observers been made, the errors in the 

 differences of longitude due to personal equa- 

 tion would in no case have been greater than 

 0.034. 



The addition of registering micrometers to 

 the transit of the Coast and Geodetic Survey 

 was considered, but this was found quite im- 

 possible in time for the trans-Pacific work. 



An exchange of observers took place between 

 San Francisco and Honolulu and difference 

 of personal equation was determined by special 

 observations as often as the observers met. 

 The results are here given. The plus sign 

 means that 8 observes later than M. 



From the exchange of observers between 

 San Francisco and Honolulu, April 20-29 and 

 June 2-13, 1903. 



/S — J!f= + 0^062 ± 0«.008. 



The following are the results from the ten 

 special nights observation: 



This result with an assigned weight of 2.0 

 combined with that determined from the ex- 

 change of observers between San Francisco 

 and Honolulu with an assigned weight of 1.3 

 gives 



8—31= + 0'^.077 ± 0^007. 



This personal equation is applied to the 

 differences of longitude between Honolulu- 

 Midway, Midway-Guam, Guam-Manila. The 

 difference of longitude between San Francisco 

 and Honolulu is corrected by the personal 

 equation determined from the exchange of ob- 

 servers only. The range of these results is 

 no greater than should be expected from the 

 computed probable errors and may, therefore, 

 be due to errors of observation rather than ta 



