November 29, 1895.] 



SCIENCE. 



725 



tude of these stars in the latitude of Hel- 

 singfors. 



Some time ago I pointed out in the As- 

 tronomical Journal that the best method of 

 investigating that portion of the optical dis- 

 tortion which depends on position angle 

 would be to photograph the stars surround- 

 ing the pole several times, with widely dif- 

 ferent readings of the hour circle. In this 

 way the quantity sought will not be de- 

 pendent on star places or proper motions, 

 and a very favorable distribution of the 

 stars can easily be secured. Such a re- 

 search can be made to fui-nish incidentally 

 a very accurate catalogue of the stars sur- 

 rounding the pole. 



Through the courtesj^ of Dr. Gill and 

 Professor Donner I have secured a collec- 

 tion of polar plates of the two poles specially 

 made for the present purpose, and I propose 

 to effect the measurement and reduction 

 of these plates at Columbia College, using 

 the Repsold photographic measuring ma- 

 chine recently presented to the College 

 by Mr. Rutherfurd Stuyvesant. The plates 

 are twelve in number for each pole, and are 

 symmetrically distributed about the pole in 

 the manner most favorable for the purpose 

 in hand. It is to be noted also that the ob- 

 servatories of the Cape and Helsingfors are 

 the most favorably situated respectively for 

 the North and South Poles. We may there- 

 fore confidently expect considerable informa- 

 tion on this difficult point, if the present 

 research can be carried to a successful con- 

 clusion. 



Other astro-photographic work going on 

 under my immediate supervision includes 

 the re-measurment of the old Eutherfurd 

 plates of the Pleiades which were discussed 

 in my paper on that group of stars. It is 

 hoped that this re-measurement will show 

 that the old plates have not deteriorated. 

 If this be the case we can proceed at once 

 to the measurement of a great number of 

 Eutherfurd plates that have never been 



measured at all. The great importance of 

 these plates arises from the fact that they 

 have a thirty-year precedence of all other 

 plates for the purpose of making a studj^ of 

 proper motions. 



Dr. Davis has been working on the re- 

 duction of the plates measured by Euther- 

 furd and has carried several clusters almost 

 to completion. These include the stars sur- 

 rounding Mu Cassiopeiae, 1830 Groom- 

 bridge, 61 Cygni, and one or two others. 

 All these are being computed in a manner 

 similar to the process used in the case of 

 the Pleiades. Dr. Davis also has in hand 

 a study of the relative masses of the two 

 components of the double star Eta Cassio- 

 peise, from the Rutherfurd measures re- 

 cently published by him. This work is 

 being done according to formulae which I 

 presented at a recent meeting of the ISTew 

 Yoi-k Academy of Sciences. Especial thanks 

 are due to Prof. J. K. Eees, director of the 

 observatory, who has done everything in 

 his power to further the prosecution of the 

 above researches. 



Among other researches of importance 

 which cannot be actively pushed at present, 

 on account of insufficient assistance, I may 

 mention the measurement and reduction of 

 a series of plates of the stars used by Gill 

 for comparison with the planet Victoria in 

 his Solar Parallax work. These plates were 

 made at the Cape Observatory aboub the 

 time of the Victoria observations, and they 

 have been placed in my hands by Dr. Gill 

 for discussion. The plates are now at 

 Columbia College. All the plates to which 

 reference has been made in this notice, ex- 

 cept Rutherfurd's, are provided with a 

 ' Eeseau,' or network of straight lines pho- 

 tographed on the plate. By the aid of this 

 reseau it is certain that we can eliminate 

 the effects of any distortion of the film dur- 

 ing development. The measurement is also 

 greatly facilitated by it. It is to be hoped 

 that Columbia College will in time possess 



