850 



SCIENCE 



[N. S. Vol. XXVIII. No. 72» 



When only a moderate degree of precision is 

 required, apparent places of the fundamental 

 stars covering a period of many years may be 

 given in very compendious form. Two tables of 

 such places will be published elsewhere, one giving 

 the coordinates of Polaris within a second of arc, 

 for a period of twenty-five years, the other show- 

 ing the apparent places of fifty equatorial stars 

 for a similar period. The probable error of a 

 right ascension for these clock stars is about two 

 tenths of a second of time. 



A New Form of Stellar Photometer: E. C. Pick- 

 ering. 



In this new form of stellar photometer, an 

 artificial star is formed by allowing a small elec- 

 tric light, run by a storage battery, to shine 

 through a minute hole, placed in the focus of a 

 small auxiliary telescope. This telescope is placed 

 at right angles to the main telescope and a piece 

 of plane glass set at an angle of 45° reflects the 

 artificial star into the eyepiece. A piece of opal 

 or ground glass is placed over the hole, and the 

 light of the artificial star is varied by moving the 

 electric light, along the axis of the small telescope, 

 by a known amount. The scale of the instrument 

 accordingly depends on the law of the square of 

 the distances, instead of on the laws of polarized 

 light, or on the empirical law found for wedge 

 photometers. 



On the Character of the Light Variations of a 

 Eerculis: Frank Schlesingee. 

 This star has long been thought to be an irreg- 

 ular variable with a period of 35 to 40 days and 

 with rapid fluctuations near minimum. Frost and 

 Adams have shown it to be a spectroscopic binary. 

 In the spring of this year it was placed upon the 

 observing program of the Mellon spectrograph of 

 the Allegheny Observatory and Professor Picker- 

 ing kindly agreed to have it observed simultane- 

 ously at Harvard with the photometer. Our 

 spectrograms were measured and reduced by Mr. 

 Baker, who deduced a period of 2.05 days for the 

 velocity variations, very difi'erent from that as- 

 signed to the light variations. In discussing these 

 observations with Mr. Baker it occurred to us 

 that the star might be an Algol variable. The 

 character of the spectrum and the form of the 

 orbit (especially the small eccentricity) and most 

 of the observations concerning its light, are in 

 conformity with this idea. Mr. Wendell's observa- 

 tions at Harvard showed that this surmise is 

 correct, and further proved the existence of a 

 secondary minimum, so that the star is more 

 properly of the Beta Lyrae type than of the Algol 



type. With the help of a diagram it may be- 

 shown how all the observed phenomena concern- 

 ing this star can be explained and how the er- 

 roneous conclusions concerning the period and the 

 fluctuations at minimum arose. The case is inter- 

 esting as showing the intimate connection between 

 photometric and spectrographic observations, the- 

 true character of the light variations being first 

 indicated by the latter. 



Photographic Light-curve of the Variable Star 



Sn Cassiopeiw: J. A. Pakkhuest. 



A lantern-slide was shown of the mean light- 

 curve of this star derived from 86 extra-focal' 

 images taken with the Zeiss 6-inch doublet be- 

 tween October 19, 1906, and April 5, 1908. The- 

 plates were measured with a Hartmann " Mikro- 

 photometer " and reduced with the writer's " ab- 

 solute scale." The observations were best repre- 

 sented by a period of 1''.9498, giving a correction 

 of — 0''.0008 to Miiller and Kempf s period. 



The range in magnitude found was 0.47, from- 

 6.52 to 6.99. Compared with Muller and Kempf'a 

 range of 0.33 (5.93 to 6.26), this gives a color- 

 intensity of 0.59 magnitude at maximum and 0.73: 

 at minimum; the difference being similar to that 

 found for other variables of short period. The- 

 star's spectrum is F 3 G on the Harvard classi- 

 fication. The radial velocity, as determined from 

 9 one-prism plates taken with the Bruce spectro- 

 graph and 40-inch refractor, is about — 7 km., 

 with but slight variation between the different 

 plates. 



This star has about the smallest range of any 

 well-attested variable, but presents no difficulties- 

 to the extra-focal method. 



(To be published in the Astrophysical Journal.) 



On the Irregularity of the Proper Motion of the 



Star Krueger 60: E. E. Barnard. 



From observations with the 40-inch refractor 

 of the Yerkes Observatory, the parallax of 

 Krueger 60 was determined. The resulting value 

 was 7r=+0".247 ± 0".010. This agrees closely 

 with the values determined by Dr. Schlesinger 

 and also with that by Dr. Russell, the three 

 values being: 



Barnard -|- 0".247 ± 0".0I0 



Schlesinger -f 0".248 ^i 0".009 

 Russell + 0".258 zp 0".013 



One of the components of Krueger 60 is aj 

 rather wide double star, found by Professor Burn- 

 ham in 1890, of the magnitude 9.3-11.0. The- 

 distance between the components is about 3i",. 



