652 



SCIENCE 



[N. S. Vol. XXXVII. Nc 956 



Magnitude 



Max. 



Cepheid variables 



Long-period variables 



Irregular variables (Spectrum M) 



Stars of Sp. O to O.5 



Stars whose spectrum shows bright 



hydrogen lines 

 Random groups of stars of spectra 



B to B.. 



4.3 



4.5 

 3.7 

 4.95 



4.53 

 3.9 

 3.7 

 3.7 



5.1 

 9.4 

 4.9 



0.015 

 0.048 

 0.060 

 0.016 



0.028 

 0.024 

 0.036 

 0.043 



0.007 

 0.073 

 0.042 

 0.006 



0.009 

 0.009 

 0.007 

 0.011 



0.004 

 0.012 

 0.015 

 0.004 



0.007 

 0.006 

 0.009 

 0.010 



—2.8 

 —0.1 

 —0.4 

 —2.0 



—1.3 



—2.2 

 —1.5 

 —1.3 



—2.0 



+4.8 

 +0.8 



Camphell's Besults 



The variable stars of spectrum M appear to be 

 much like the general run of stars of this spectral 

 class in distance, peculiar velocity and (at maxi- 

 mum) in brightness, being then about 100 times 

 as bright as the sun. At minimum, the average 

 long-period variable seems to be comparable with 

 the sun in brightness. 



Stars of Class B, showing bright hydrogen lines, 

 do not differ materially in distance, brightness or 

 peculiar velocity from those that do not, and stars 

 of spectrum O are but little farther away or 

 brighter. 



The Cepheid variables, on the contrary, are very 

 much farther away, brighter and more slowly 

 moving than most stars of Classes F or G, and 

 closely resemble the Orion stars in all these re- 

 spects, and also in their strong condensation to- 

 ward the Milky Way — so much so as to suggest 

 some real relation between them. Even at mini- 

 mum, these stars average some 400 times as bright 

 as the sun. If they are comparable with it in sur- 

 face brightness, as seems very probable, their 

 diameters must be at least ten times the sun's — ■ 

 far larger than their spectroscopic orbits. If their 

 average density was less than 1/1200 that of the 

 sun, their companions would collide with them at 

 periastron. It follows that the larger components 

 of these systems must be more massive than the 

 sun, and the invisible companions' of the order of 

 one tenth the mass of their primaries — as Camp- 

 bell has anticipated. 



The great brightness of all these variable stars 

 seems a very serious objection to any theory which 

 represents them as stars nearing extinction, but 



unfortunately, does not itself suggest any theory 

 of their nature. 



The Jupiter Perturbations of the Group of Small 



Planets, 11:= 2/5: D. T. Wilson. 



Tables have been constructed by the Hansen- 

 Bohlin method for the computation of the per- 

 turbations of Jupiter on the group of small plan- 

 ets whose mean daily motions are in the neighbor- 

 hood of 750". The perturbations of Pandora 55, 

 of Bellona 28 and of Johanna 127 have been 

 computed and the results compared with those of 

 the same planets computed by Hansen 's method 

 by Messrs. M'oller, Bohlin and Olsson. 



Correcting and Testing Micrometer Screivs: Wm. 

 Gaertner. 

 Read by title. 



The Temperature assigned by Langley to the 



Moon: Frank W. Vert. 



Langley 's opinions in regard to the temperature 

 of the lunar surface in sunshine varied widely at 

 different times, but in the main he favored a low 

 temperature. 



The foundation of this opinion is examined and 

 is shown to be invalid. Incidentally, statements 

 by other investigators, which are based to some 

 extent on Langley 's opinion, are discussed. 



The paper will be published in Science. 



At the end of the last session a resolution was 

 adopted expressing the thanks of the society to 

 the authorities of Case School and other friends 

 in Cleveland for the hospitality and privileges 

 extended to the members of the Society. 



Philip Pox, 

 Secretary 



