128 



SCIENCE. 



[N. S. Vol. XII. No. 291. 



smallest value with Eros in the present op- 

 position is only 28 degrees, and its greatest 

 value more than twice that amount. In 

 the observations of the oppositions of our 

 moon the formula of simple proportion is 

 appreciably changed before reaching that 

 extent. If the formula depends upon the 

 diminution of light in arithmetical progres- 

 sion, the variation is in one direction, 

 whereas if it depends upon diminution of 

 light measured in magnitudes, or in geo- 

 metrical progression, the variation is in the 

 opposite direction. It has seemed to me 

 desirable that special pains should be taken 

 to observe Eros photometrically, in order 

 to learn what we can of the true law of di- 

 minution, and if possible its cause. 



I desire especially to call attention to this 

 desirability, for the reason that a tall build- 

 ing is iu process of erection so close to 

 my observatory that should it be com- 

 pleted early in the present year, it may pre- 

 vent my photometric observation of Eros 

 at the times essential to this investigation ; 

 in which case we must rely wholly upon 

 such observations as may be made else- 

 where. I had already made preliminary 

 observations in anticipation of this investi- 

 gation before the building was commenced ; 

 and I still hope that I may be able to com- 

 plete my work before my observation of 

 that part of the sky is cut off. 



Standards for Faint Stellar Magnitudes : By E. 



C. Pickering. 



It is believed that the following extract 

 from the report of Professor Cross, the 

 Chairman of the Rumford Committee of the 

 American Academy, will be of interest to 

 members of the Astrophysical Society. 



An appropriation of five hundred (8500) 

 dollars has been made from the Eumford 

 Fund to be expended under the direction of 

 Professor Pickering, for the purpose of 

 carrying, out an investigation on the bright- 

 ness of faint stars by co-operation with 



certain observatories possessing large tele- 

 scopes. This appropriation results from a 

 communication made to the Council of the 

 American Astronomical and Astrophysical 

 Society held in New York last January. 

 It was represented that the most urgent 

 need of astronomy in America was adequate 

 endowment of the great telescopes of the 

 country so that they could be kept actively 

 at work. It was shown that while the two 

 largest telescopes of the country, and of the 

 world, were kept constantly at work the 

 means for the reduction and publication 

 of the observations is wholly inadequate, 

 while some of the largest telescopes in the 

 country, representing a plant costing hun- 

 dreds of thousands of dollars, are nearly 

 idle and therefore useless. Observations of 

 the greatest value can be obtained with 

 these instruments at small expense, and 

 it is hoped that the beginning now made 

 will justify its permanent continuance on a 

 large scale. The problem undertaken is 

 the determination of the light of faint stars, 

 selected as standards. These will furnish 

 points of reference to which other photo- 

 metric measures may be referred. Five 

 photometers have been constructed in which 

 by interposing a photographic wedge of 

 shade glass, an artificial star is reduced in 

 brightness until it appears equal to a real 

 star, as seen in a large telescope. Thirty- 

 six regions have been selected in different 

 parts of the sky, in each of which a series 

 of standards is to be measured. Five stars 

 of about the twelfth magnitude, five of the 

 fifteenth, five of the sixteenth, and five of 

 the seventeenth, are to be chosen in each 

 of these regions. The faintest stars will be 

 selected and measured with the Yerkes 40- 

 inch and Lick 36-inch telescope. Those of 

 the sixteenth magnitude will be measured 

 with the 26-inch telescope of the University 

 of Virginia and perhaps the Princeton 23- 

 inch telescope. The stars of the fifteenth 

 magnitude will be measured with the 15- 



