878 



SCIENCE 



[N. S. Vol. XXXI. No. 805 



For the entire cruise important corrections were 

 also disclosed for the charts which give the lines 

 of equal magnetic dip and of equal magnetic 

 force. 



The Carnegie is now heing fitted out for a cir- 

 cumnavigation cruise of about three years. Mean- 

 time, the magnetic surveys of unexplored coun- 

 tries are pushed, so that it is confidently expected 

 that by the year 1915 the general magnetic survey 

 of the greater part of the globe will have been 

 completed in sufficient detail to permit the con- 

 struction and issuing of a new set of magnetic 

 charts. 

 Spectra of Recent Comets: Edwin B. Feost, 



Williams Bay, Wis. 



On the Distances of Red Stars: Henbt Noeeis 



Russell, Princeton. 



Comparison of the parallaxes of stars, derived 

 by the writer from photographs taken at the 

 Cambridge Observatory (England) by Mr. A. R. 

 Hinks and himself, and their spectra, determined 

 at Harvard under the direction of Professor Pick- 

 ering, shows a marked correlation between spec- 

 tral type and parallax. 



The proportion of orange and red stars (types 

 K and M) among those of large proper motion, 

 and especially among those shown by direct meas- 

 urement to be our near neighbors, is very much 

 greater than among the general run of stars of 

 the same apparent brightness. Conversely, stars 

 of the same apparent brightness and proper mo- 

 tion average nearer to u the redder they are. 



It follows that these stars are intrinsically 

 fainter the redder they are, the reddest ones av- 

 eraging only one fiftieth as bright as the sun. 

 On the other hand, many bright red stars (such 

 as Arcturus) are at great distances, and are 

 actually at least one hundred times as bright as 

 the sun. 



All this can be explained on the hypothesis 

 (now well established on other grounds) that the 

 reddest stars are the lowest in temperature. With 

 the latest determinations of temperature and sur- 

 face brightness, it appears that the fainter red 

 stars are somewhat smaller, and presumably 

 denser, than the sun, while the brighter ones are 

 very much larger than the sun, and presumably 

 of very small density. The latter class probably 

 represent an early stage of evolution, and the 

 former the latest stage that can be observed. 



A Standard System of Photographic Stellar Mag- 

 nitudes: Edwaed C. Pickeeing, Cambridge. 

 Since 1879, about two million photometric ob- 



servations of one hundred thousand stars have 

 been made at the Harvard College Observatory. 

 The results, published in volumes 50, 54 and 70 

 of the Harvard Annals, furnish a standard scale 

 for determining the brightness of the stars in all 

 parts of the sky, according to a uniform system. 



The general introduction of photography in 

 nearly all departments of astronomy has created 

 an urgent need for a similar scale to give the 

 photographic magnitudes of the stars. The two 

 scales will differ, since red or yellow stars will 

 always photograph faint. The scale proposed will 

 be the same for white stars as the visual scale. 

 Three methods are adopted in this work for deter- 

 mining the photographic brightness. First, cor- 

 recting the visual magnitude by the class of 

 spectrum. Secondly, by measuring with great 

 care the photographic brightness of a sequence of 

 stars near the north pole, and superposing this 

 photographically on the stars to be measured. 

 Thirdly, by attaching to the object glass of the 

 telescope a small prism, a second image of each 

 star, five magnitudes fainter than the principal 

 image, is formed. 



All three of these methods are in use on a large 

 scale at the Harvard Observatory, and it is hoped 

 that, as the result of many thousand measures, 

 a satisfactory solution of the problem will be 

 found. 



The Existence of Planets about the Fixed Stars: 

 T. J. J. See, Mare Island, Cal. (Read by title.) 



Results of Recent Researches in Cosmical Evolu- 

 tion: T. J. J. See, Mare Island, Cal. (Read by 

 title.) 



Some Interesting Double Stars: Eeic Doolittle, 



Philadelphia. 



The many thousand double stars in the sky may 

 be divided into two classes. There are some in 

 which the two stars are not really near each other, 

 but which merely happen to lie in the same 

 direction as viewed from the earth, and there are 

 others which form true systems composed of two 

 suns revolving about their common center of 

 gravity. In the latter case, measures show that 

 one sun revolves about the other in an elliptic 

 orbit. It often happens that a very few measures 

 of such a system secured at certain critical times 

 throw unusual light on the nature of the motion 

 and the size of the orbit. This is especially the 

 case when the companion star apparently ceases 

 its motion in one direction and begins to move 

 backward, and also when the companion is pass- 

 ing nearest the principal star. Several diagrams 



