82 H. JAC0BY, PHOTOGRAPHIC RESEARCHES NEAR THE POLE OF THE HEAVENS. 



5. Conclusion. 



In conclusion, let us summarize briefly the results obtained in the 



present paper. These results are: „ 



1. A method of reduction for ordinary astronomical photographs 



whose centres are within about 1° of the pole. 



2. A method of reduction for polar trail plates. 



3. An application of this method to an example, based upon an 



actual plate. 



4. The outline of a method for determining the constants of preces- 

 sion, nutation, and aberration from trail plate observations. 



5. Perhaps we cannot consider the superiority of the trail plates 

 over other methods proven, because we have not yet discussed a 

 sufficiently large number of such plates. But we can at least con- 

 clude that the methods here deduced will be found of some help, 

 if the trail plates should finally come to be used in astronomical 

 research. 



I cannot close this paper, which has occupied most of my spare time 

 for two years, without expressing my hearty thanks to the many persons who 

 have aided me in its preparation. MissF.E. Harpham and MissK. U. Peirce 



executed the measures for the example with care and skill, and Miss Harpham, 

 assisted byMissEudora Magill, has had a large share in the computations: 

 Miss C. E. Furness, of Vassar College, lias examined carefully the first part 

 of the paper, and has suggested various corrections, especially in connection 

 with the small refraction terms involving the auxiliaries I and J. I am 

 indebted to Mr. Frank Schlesinger, one of the students of astronomy at 

 Columbia University, for much helpful discussion. To Prof. Donner, of Hel- 

 singfors, my especial thanks are due. He studied the first draft of my work, 

 and has made many valuable suggestions. To him I also owe the plate used 

 in the example. I likewise owe much to the encouragement received from 

 Dr. Gill, of the Cape of Good Hope, Prof.E C.Pickering, of Harvard, and 

 Dr. Backlund, of Pulkowo. Finally, I return grateful thanks to Prof. J. K. 



Rees, of Columbia 



eady 



placed at my disposal the resources of the Columbia Observatory 



S**«r 



4>iu.-MaT. cTp. 82. , 2 



