200 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. X, NO. 7. 



Several interruptions, of which one lasted for nearly a year, were caused by the resignation 

 of assistants who were called to permanent positions elsewhere. Thus Doctor Crawford, Doctor 

 Ross, Doctor Newkirk, and Miss Kobe were lost in turn to the work. Other interruptions arose 

 from the necessity of temporarily employing the Watson computers as assistants in the regular 

 departmental work of instruction. So far three distinct sets of computers have been trained 

 in succession for the work. At present, the investigations are progressing with Miss Estelle 

 Glancy, a graduate'student in the university, as chief computer. 



The original program, which included only those planets for which the investigation of the 

 general perturbations had not been undertaken by other astronomers, has since been extended 

 by the trustees, at their own initiative, to embrace the publication of tables of all of the 

 twenty-two Watson planets excepting (132) Aeihra, which is lost. Investigations, however, 

 by Mr. A. J. Champreux, which are under way, point to the possibility of deciding the fate of 

 this planet. 



To enable the author to prepare all the available material for publication, the Watson 

 trustees placed in his hands such original computations and manuscripts as were in their pos- 

 session. These included, in the main, perturbations and tables of (103) Hera and (119) Althaea 

 by William McKnight Ritter; perturbations and tables of (93) Minerva by Dr. W. S. 

 Eichelberger; perturbations of (101) Helena by Ritter, tables by Eichelberger, and 

 fragments of a comparison between theory and observation by G. K. Lawton; development 

 of the perturbations and partial comparison between theory and observation for (79) Eurynome 

 by Prof. E. Becker, continued by Ritter. 



In regard to these planets, the trustees desired that certain discrepancies between theory 

 and observation should be investigated, that such revision of the results be made as might seem 

 necessary, and that the tables which in general gave the theoretical positions to a tenth of a 

 second of arc, should be abridged to correspond to the limits of accuracy fixed by the method 

 of investigation used in each case. 



This task proved far more laborious than was anticipated. In the case of (93) Minerva 

 the perturbations were checked by a complete independent development. Yet, it has ulti- 

 mately been possible to preserve, in the main, the original results of the author's predecessors 

 in the work, and thus to secure for them the credit which is their due. No change whatever 

 has been made in Eichelberger' s results on (93) Minerva. 



The aim of the trustees was not that a theoretical study should be undertaken of the rela- 

 tive merits of the various methods of developing the perturbations of the minor planets, but 

 that tables of the Watson planets be produced in the most expeditious manner. It was there- 

 fore not within the scope of this work to arrange for practical application to the minor planets 

 such analytical methods as have been made available by Poincare, E. W. Brown, and others, 

 in a manner similar to that employed by Brendel in his "Theorie der Kleinen Planeten," 

 which is based on Gylden's researches. 



Furthermore, Hansen's and Bohlin's methods have so far been found eminently suitable 

 for the objects aimed at. Nevertheless, the details of. the investigation to be published later 

 will furnish abundant material for studies of a purely analytical nature. 



The length of time required to develop perturbations by Hansen's method is not such an 

 important factor after all in these considerations, for after gaining the necessary experience 

 Crawford and Ross were able to completely develop the perturbations of the first order in 

 normal cases in from forty to sixty hours. 



For three, planets of the Hecuba type the development of the perturbations remains to be 

 made. Preparatory to this, special tables for the group i have been computed on the basis 

 of the method employed by Bohlin for the group J in his "Formeln und Tafeln zur gruppen- 

 wrisse Berechnung der allgemeinen Storungen benachbarter Planeten" and "Sur le developpe- 

 ment des Perturbations Planetaiics." 



The tables for the group \ were barely completed when similar tables by H. von Zeipel 

 appeared in the Memoires de I'Academie Imp6riale des Sciences de St. Petersbourg, VIII serie, 



