334 



SCIENCE. 



[N. S. Vol. XVII. No. 426. 



Preliminary Note on the Total Light of the 



Stars: Sidney D. Townley. 



While engaged in photometric work at 

 the Lick Observatory during the past sum- 

 mer a few experiments were made to de- 

 termine the amount of light received from 

 the sky at night when the moon is not shin- 

 ing. This work was undertaken at the 

 request of Director Campbell, to whom the 

 problem was suggested by Professor New- 

 comb. 



Both visual and photographic methods 

 are applicable to the solution of this prob- 

 lem, and Professor Newcomb has already 

 employed some of the visual methods, the 

 results of which were printed in the Astro- 

 physical Journal, December, 1901. My 

 efforts were directed almost exclusively to 

 perfecting a photograpliic method. The 

 results thus far obtained are meager, but 

 it is believed that a reliable method has 

 been found. 



The method adopted is, indeed, very 

 simple. Both lenses were removed from 

 the Crocker photographic telescope and a 

 cardboard cap of three centimeters diam- 

 eter attached to the end of the telescope 

 tube. An exposure of one hour was made 

 upon a bright star and the result was, of 

 course, an impression on the plate of the 

 size and shape of the aperture. Exposures 

 were then made upon the sky by means of 

 four camera boxes, consisting simply of 

 aperture and plate, attached to a polar 

 axis made of a piece of 4 x 4. The angular 

 apertures used varied from five to ten de- 

 grees. The five plates were developed at 

 the same time in a large tray, and their 

 relative intensities measured by means of 

 a Luimner-Brodhun photometer. 



In the very limited length of time which 

 I had to devote to this work it was possible 

 to obtain only a few sets of plates. Two 

 of these sets give reliable results. In each 

 Vega was the comparison star used. In 



the one the camera boxes were directed to 

 the sky about half way between y Pegasi 

 and /? Ceti, in the other to the Milky Way 

 nearest Vega. 



The results are, from the first, that the 

 light of Vega is equivalent in actinic in- 

 tensity to the light received from an area 

 of rather vacant non-galaetic sky 7° 16'. 4 

 in diameter, from the second, that the light 

 of Vega is equivalent to the light received 

 from an area of galactic sky 5° 19'. 8 in 

 diameter. This gives galactic sky to be 

 1.9 times brighter than non-gdlactic sky. 

 If we take the magnitude of Vega to be 

 0.2, then from the first result we find that 

 the light received from an area of non- 

 galaetic sky one degree in diameter is 

 equal to the light of a 4.5 magnitude star, 

 which is not far from the result obtained 

 by Professor Newcomb, namely, that the 

 light received from an area of non-galaetic 

 sky one degree in diameter is equal to 0.9 

 the light of 5.0 magnitude star. 



Photometric and Photographic Observa- 

 tions of Faint Variable Stars: J. A. 

 Parkhukst. 



In the course of this work at the Yerkes 

 Observatory several stars have been found 

 whose brightness at minimum is at or be- 

 low the limit of the 40-inch refractor. To 

 illustrate three specimen fields, lantern 

 slides were prepared from negatives taken 

 with the 24-ineh reflector, covering a field 

 of 30' around the variable, corresponding 

 to the inner square of Hagen's charts. 



7220 S Cygni.—Fl&te taken November 

 24, 1902, exposure 61 minutes. The vari- 

 able is about 11th magnitude; its greatest 

 range of variation is from the 8th to the 

 16th magnitude, being approximately equal 

 at maximum to the star 1' north, and at 

 minimum to the star 0'.5 preceding. 



7458 V Delphini.— Plate taken Septem- 

 ber 7, 1902, exposure 68 minutes. This 

 star has perhaps the greatest range of any 



