44 



ASTRONOMY, PROGRESS OF, IN 1890. 



moving toward and the other from us, the K 

 line in the spectrum of the former will be dis- 

 placed toward the violet, and in the latter in 

 the direction of the red, thus causing the line 

 on the plate to be seen double. Of course, in 

 part of their orbital revolutions (at their con- 

 junct ions) the two stars will be moving laterally 

 and tin- lint- will appear single, but at elonga- 

 tions when moving toward or from us will be 

 s.-.-ii double. It is this which causes the peri- 

 odical doubling of the lines, and proves that, 

 though telescopically single, the star is spectro- 

 photographically double. 



It has long been known that the waves of 

 light at the violet end of the spectrum are 

 more numerous and shorter, and more refrangi- 

 ble, than those at the red end. It follows, 

 then-fore, that if a luminous body is approach- 

 ing us more waves will be crowded into a given 

 space, and thev will be shorter than if it is at 

 rest, and all the lines in its spectrum will be 

 slightly moved toward the violet ; while, on the 

 com ra'ry. if it be moving from us, the waves will 

 be longer and fewer, and the lines will be dis- 

 placed toward the red. An ingenious application 

 of this principle to determine the period of the 

 sun's rotation, has been often and successfully 

 tried, confirmatory of the assumed correctness 

 of the period assigned by observation of his 

 spnts. The two poles of the sun, by virtue of 

 the sun's rotation, have no motion whatever 

 toward or from the earth, and therefore the lines 

 in the polar spectra ought not to show any dis- 

 placement, and do not. If the spectroscope be 

 pointed to the east limb of the sun which is 

 approaching us, all the lines (save, of course, the 

 air lines) will be displaced toward the violet end 

 of the spectrum. If it be turned toward the 

 west limb, which by rotation is moving from the 

 earth, all the solar lines from that region will 

 show displacement toward the red. 



Prof. James E. Keeler, of the Lick Observatory, 

 has determined the rate of motion of several 

 planetary nebulae in our line of sight. The 

 brightest nebular line, the origin of which is un- 

 known, was used for comparison. Of the ten 

 examined, two are approaching the earth, 17'2 

 and :J1-0, and two receding 1G'8 and 38*4 miles a 

 second respectively. These deductions are con- 

 sidered by astronomers of great importance. 

 Hi- paper is published in No. 11 of the publica- 

 tion- of tin- Astronomical Society of the Pacific. 



Orbit of Algol. Astronomers have long en- 

 tertained the opinion that the variation in the 

 brightness of Algol is due to periodic transits of 

 a dark companion across, or partly across, the 

 face of the I. right star as seen from the earth. 

 Prof. Vogel, of the Potsdam Observatory, Prus- 

 sia, act ing on the suites! ion of Prof. Pickering, 

 who thought its orbit might, bo, determined by 

 photO-Speotroeoopifl observation, made six pho- 

 t "graph- of the spectrum of Algol, three before 

 minimum periods and three after, there being an 

 interval of several months between them. The 

 three taken before minimum show the lines de- 

 cidedly displaced toward the red end of the spec- 

 trum, while the others are moved in the direction 

 of the violet. I-" rom careful measurements of the 

 plates he makes the motion and recession of the 

 s tar to be about. p<|iial. amount ing to about 27 

 miles a second. Assuming circular orbits in a 



plane parallel to. our line of sight and a central 

 transit, he derives the following elements for the 

 system : Diameter of Algol, 1,074,100 miles ; di- 

 ameter of its companion, 840,000 miles ; distance 

 of centers, 3,269,000 miles ; velocity of Algol per 

 second, 27 miles ; velocity of its companion per 

 second, 56 miles; translation of Algol system 

 toward sun per second, 25 miles ; mass of Al- 

 gol sun = 1 = f ; mass of its companion sun 



Dark Stars. From what has been said, the 

 following three conclusions are deducible : (a) If 

 a bright star give a system of lines neither double 

 nor hazy, though showing periodic spectral dis- 

 placement, it is manifest that it is a double, with 

 one component bright and the other dark, the 

 former producing the spectrum and the latter 

 causing it alternately to approach and recede 

 from the earth by the revolution of each around 

 the center of gravity of the system, in a plane 

 that passes through the earth or, at least, not 

 perpendicular to the line of sight. (6) Should a 

 star be periodically displaced and also darkened, 

 it shows that the dark companion star transits 

 the bright one, and it would be classed as a va- 

 riable like Algol and many others of that type, 

 (c) If a line from the spectrum of a star be peri- 

 odically doubled, it follows that both components 

 are bright and produce the same spectrum. Prof. 

 Vogel does not regard the companion of Algol 

 as absolutely dark, though from want of in- 

 trinsic brightness it is incapable of producing a 

 spectrum which, were its albedo -fa of that of 

 Algol, it would do. 



Alpha Virginia (Spica) appears as a photo- 

 spectrographic variable of short period, the com- 

 panion being a dark star or, at least, one too 

 faint to form a visible spectrum. Therefore, the 

 only inference of its duplicity is the periodic va- 

 riation of brilliancy and the movement of the 

 lines in the spectrum of the bright star only, in- 

 stead of opposite separations of the lines in each 

 star, as in the case of Zeta Ursa?, etc. The period 

 of Spica is about four days, with an orbital ve- 

 locity of 56 miles a second. 



Benefactions. Miss C. W. Bruce, of New 

 York, who recently gave $50,000 to Harvard 

 College Observatory for the purchase and main- 

 tenance of a photographic telescope, has given 

 $6,000 additional for the promotion of original 

 astronomical research, placing it in the hands of 

 Prof. Pickering for disbursement, who is to be- 

 stow, it, in sums not exceeding $500, upon such 

 applicants, individuals or institutions, as have 

 met certain required conditions. The late Prof. 

 Elias Loomis bequeathed more than $300,000 in 

 trust to Yale University, which, at the death of 

 his two sons, will be conveyed to that institution. 



Prizes and Honors. The Janssen prize was 

 bestowed by the French Academy upon Norman 

 Lockyer. The Donohoe comet medal No. 1 was 

 awarded to William R. Brooks, for the discovery 

 of comet I 1890. The Council of the Royal 

 Astronomical Society of England awarded no 

 medal in 1889. The last official documents 

 signed by Dom Pedro, ex-Emperor of Brazil, 

 were those conferring on Admiral Mouchez and 

 M. M. Janssen and Perrotin the grade of officer 

 of the Order of the Rose of Brazil, and on M. M. 

 Frassenet and the brothers Henry knighthood 

 of the same order. 



