Januabt 22, 1909] 



SCIENCE 



155 



was discontinued, and practically no observations 

 have been made with it since that time. In 1906 

 a transit micrometer made by Warner & Swasey 

 was substituted for the old eye-end and a few 

 practise observations were made by various ob- 

 servers. 



The plan for the future work of the instrument 

 is given in a general way in the report of the 

 superintendent of the U. S. Naval Observatory 

 for the fiscal year ending June 30, 1908, which has 

 just been issued. This plan involves an attempt 

 to render the observations of the sun and fixed 

 stars and, consequently, of all bodies which are 

 referred to them, of as strictly fundamental a 

 character as is practicable. 



The importance of such work to the science of 

 astronomy and in the plan of work of an observa- 

 tory maintained by the government is generally 

 recognized by astronomers. It is expensive and 

 laborious and in some respects perhaps less at- 

 tractive than some other kinds of astronomical 

 work in that it can not excite the interest or 

 occupy the attention of the general public to any 

 great extent. But for its proper performance, 

 technical qualifications of a high order are re- 

 quired. Partly for these reasons, no doubt, this 

 work has, with a few notable exceptions, not been 

 as efiiciently done in the observatories of the 

 world generally for many years as is needed for 

 the advancement of astronomy. 



All accurate observations of the positions of the 

 planets depend on this work and it thus becomes 

 in some degree necessary for the further advance- 

 ment of celestial mechanics. It is equally impor- 

 tant for the solution of that greatest problem of 

 physical science, the constitution of the visible 

 universe, which must perhaps wait on further 

 lapse of time and increase in accuracy of the 

 observations of the places of the stars. 



The late Professor Asaph Hall, U.S.lSr., was 

 much interested in this kind of astronomical work, 

 as may be seen by consulting the Ast. Naoh., No. 

 1692. 



6. The problems treated in the paper by Pro- 

 fessor Moulton are : ( 1 ) The theoretical shape of 

 the sun, (2) the character and period of its pos- 

 sible gravitational oscillations, (3) the effects of 

 changes of its dimensions upon its rate of rota- 

 tion, (4) its energy of rotation, (5) its potential 

 energy, (6) its temperature and rate of rotation 

 and ( 7 ) applications of the same ideas to variable 

 stars. 



The results are: (1) the sun is oblate and the 

 theoretical difference in its polar and equatorial 

 diameters is less than 0".01. (2) Its gravita- 



tional oscillations are expressible in spherical 

 harmonics whose periods depend upon their order. 

 Assuming the sun to be a homogeneous liquid, the 

 longest period is 3 h. 8 m. If it has the viscosity 

 of water this oscillation will change to 37 per 

 cent, of its value in 2.2 X 10'° years. (3) The 

 change of the sun's diameter by 0".l will change 

 its period of rotation by 7.8 minutes. (4) The 

 formula was found for the change in the rota- 

 tional energy. (5) The formula for the potential 

 of spheroid of polar radius c, equatorial c V 1 + ^^ 

 and mass m upon itself is 



y = |fc=.OTVo(l — JV — ^yX*...). 



(6) The expansion of the sun by 0".l will de- 

 crease its temperature (assuming its specific heat 

 is unity) more than 1,400° C, and if it obeys 

 Stefan's law, diminish its radiation (assuming its 

 temperature to be 6,000° before expansion) by 

 more than 65 per cent. (7) It is shown how 

 gravitational oscillations can explain many puz- 

 zling phenomena of variable stars, such as vari- 

 able periods in the so-called eclipse variables, 

 secondary maxima and minima, varying maxima 

 and minima, etc. It is thought that these factors 

 are supplementary even in those cases where the 

 binary character of the star is certain, and that 

 perhaps in certain classes of stars they may be 

 the only causes of variability. 



7. Spectroscopic binaries of the helium type 

 may be divided for convenience into two classes: 

 those of long period and high eccentricity, and 

 secondly, those whose periods are short and whose 

 orbits are nearly circular. Mr. Baker's paper 

 relates to the latter and much more numerous 

 class, of which a Yirginis is typical. This class 

 includes a large number of Algol variables, as a 

 special case where the orbital inclination ap- 

 proaches 90°, if the eclipse theory of their light 

 variation be assumed. The following conclusions 

 were reached: The majority of spectroscopic bi- 

 naries of the helium type belong to one class, 

 they revolve in close proximity in nearly circular 

 orbits of short period, they are Algol variables 

 inclined at various angles, the spectra of both 

 components are, in general, visible and similar, 

 and the fainter components are less massive than 

 the brighter ones. 



8. The binary character of a Goronce Borealis 

 (0=15" 30"', S=-t-27° 3') was discovered by 

 Hartmann from six plates obtained at Potsdam 

 in 1902 and 1903. The spectrum is of the type 

 1 a 2 in the Vogel classification. 



One hundred and thirty-seven plates of this star 

 were obtained at Allegheny Observatory between 



