May 6, 1904.] 



SCIENCE. 



719 



The Reflex ZenUk Tube: Professor Chas. 



L. DooLiTTLE, Philadelphia. 



More than fifty years ago an instrument 

 known by this name was constructed from 

 designs by Mr. J. B. Airy for use at Green- 

 wich. The instrument consists of a tele- 

 scope fixed in a vertical position. A basin 

 of mercury below the objective at a dis- 

 tance equal to one half its focal length 

 reflects the rays from a zenith star up- 

 wards, bringing them to a focus immedi- 

 ately in front of the objective. A microm- 

 eter thread moving in the focal plane 

 furnishes the means of measuring the posi- 

 tions of stars which culminate sufficiently 

 near the zenith to be within the field of 

 view. The instrument was designed es- 

 pecially for use with y Draconis, which 

 culminated very near the zenith of Green- 

 wich. The object was a more accurate de- 

 termination of the constant of aberration, 

 and incidentally the star's parallax. So 

 far as known this is the only instrument 

 of this description ever constructed. 



In the course of the long series of lati- 

 tude observations carried on at South 

 Bethlehem, and afterwards at this place, 

 anomalous results have appeared from time 

 to time which seem to merit further study. 

 The practical method for attacking the 

 problem appears to be to carry on two 

 series, of observations simultaneously, em- 

 ploying two instruments of different con- 

 struction. "With this in view Mr. Joseph 

 Wharton has generously provided the 

 means for installing a reflex zenith tube of 

 eight inches aperture at this place. War- 

 ner and Swasey have this instrument well 

 advanced and it is hoped that it may be in 

 practical operation at an early day. 



It will be used in connection with the 

 zenith telescope, which has been thoroughly 

 renovated and the optical power increased 

 so that stars as faint as the eighth magni- 

 tude may be employed. It is hoped that 

 simultaneous observations with the two in- 



struments may be carried on for two or 



three yeai's at least. 



Faint Double Stars: Mr. Ekic Doolittle, 



Philadelphia. 



The table of limiting distances given by 

 Mr. R. T. A. Innes, ■ within which a pair of 

 stars is to be considered as a double star 

 and entered into the catalogTies, was ex- 

 amined, and the opinion was expressed that 

 the limits of this table were too narrow. 

 In support of this opinion it was pointed 

 out that of the 175 Burnham stars known 

 to be binary, 16 would have been ex- 

 cluded by the above criterion, and atten- 

 tion was called to the triple systems /j. 

 Herculis and o Eridani, which exceed the 

 limits of the table. The 1,290 Burnham 

 stars were examined as to proper motion, 

 and it was shown that an average of 8 out 

 of 51 minute stars measured in the vicinity 

 of a bright star have an independent 

 proper motion of their own, while an aver- 

 age of 27 out of 51 are carried along with 

 the bright star; the stars examined in each 

 case exceeded the limits of the above table. 

 It was pointed out that many eases of 

 proper and orbital motion might, therefore, 

 reasonably be expected among the faint 

 stars, and the importance was urged of se- 

 curing an initial series of measures to serve 

 as a basis for the investigation of their 

 f utux-e motion. 



New elements of /a Herculis were given, 

 and the recent measures of this system and 

 of Krueger 60 and o Eridani secured at 

 the Flower Observatory were referred to. 



On the Spectra- and General Nature of 

 Temporary Stars (with lantern slide 

 illustrations) : Professor William W. 

 Campbell, Mt. Hamilton, Gal. 

 Our knowledge of the visual spectrum 

 of the Orion nebula began with the invalu- 

 able pioneer observations of 1864^65 by Sir 

 William Huggins. The first photographs 



