40 



ASTRONOMICAL PHENOMENA AND PROGRESS. 



clocks will bo provided for the ten telescopes last 

 referred to. These ten clocks are not required to be 

 of the same quality as the five used with the transit- 

 instruments ; though they will all be trustworthy 

 tiuie-measurers. It is also unnecessary that they 

 should be timed and rated long before the observa- 

 tions are to be made during which they will be 

 employed. 



The United States commissioners appointed 

 to supervise the transit observations are Rear- 

 Admiral Sands (president), and Profs. New- 

 comb and Harkness, all connected with the 

 Naval Observatory. The congressional appro- 

 priation of $50,000 for the purchase of instru- 

 ments is in their hands. They intend to equip 

 eight photographic stations four in China, 

 Japan, and (probably) in one of the islands ad- 

 jacent to Japan ; and four in New Zealand, 

 Chatham Island, Tasmania, and Kerguelen 

 Island. A meeting of all persons who will 

 take part in the work will be held in Washing- 

 ton in the spring of 1874, for rehearsal and 

 practice. The commissioners will have an 

 " artificial Venus," making a transit over an 

 artificial sun, at a distance of two miles, and 

 all the observers will use, on that occasion, the 

 same instruments which they will employ in 

 taking note of the real transit of Venus. 



The Disintegration of Comets. Prof. Daniel 

 Kirk wood, of Iowa, contributes to Nature a 

 paper on this topic. He undertakes to present 

 historical evidence of the gradual disintegra- 

 tion of periodic comets. He refers, for proof, 

 to what is known of the comets of A. D. 389, 

 416, 813, 896, 1532, 1618, and 1661. Coming 

 down to later days, he cites the bipartition of 

 Biela's comet in 1845, and the non-appearance 

 of the two fragments in 1865, and concludes 

 as follows : " The comet of Halley, if we may 

 credit the descriptions given by ancient writers, 

 has been decreasing in brilliancy from age to 

 age. The same is true in regard to several 

 others believed to be periodic. The comet of 

 A. D. 1097 had a tail 50 long. At its return, 

 in March, 1840, the length of its tail was only 

 5. The third comet of 1790, and the first of 

 1825, are supposed, from the similarity of their 

 elements, to be identical. Each perihelion 

 passage occurred in May, yet the tail at the 

 former appearance was 4 in length, at the 

 latter but 2|-. In short, instances are not 

 wanting of this apparent gradual dissolu- 

 tion. It would seem, indeed, extremely im- 

 probable that the particles driven off from 

 comets in their approach to the sun, forming 

 tails extending millions of miles from the prin- 

 cipal mass, should again be collected around 

 the same nuclei. 



The fact, then, that comets and meteors 

 move in the same orbits, is but a consequence 

 of that disruptive process so clearly indicated 

 by the phenomena described. In this view of 

 the subject, comets even such as move in 

 elliptic orbits are not to be regarded as per- 

 manent members of the solar system. Their 

 debris, however, thus scattered through space, 

 and subject more or less to planetary peritur~ 



bation, may casually penetrate the atmosphere, 

 producing the phenomena of sporadic meteors. 



The researches of Signer Schiaparelli cor- 

 roborate the theory advanced by Prof. Kirk- 

 wood. The former suggested that the force 

 which broke up the comets was simply the 

 unequal attraction of the sun on different por- 

 tions of the nebulous mass ; but other astron- 

 omers incline to the opinion that it is a cosmi- 

 cal force of repulsion. 



See COMET (BIBLA'S). 



The Motions of Stars. Dr. William Huggins 

 has been following up his profound investiga- 

 tions into the motion of stars, as revealed by 

 the spectroscope. Better instruments have 

 warranted him in correcting some of the con- 

 clusions which he formerly gave out. He now 

 thinks that Sirius is travelling from the earth 

 at a rate of from 18 to 22 miles per second 

 instead of from 26 to 36 miles as previously 

 announced by him. The apparent rate of mo- 

 tion observed in the star Betelgeux (going from 

 the earth) is estimated at 37 miles per second. 

 Rigel is supposed to be receding at the rate of 

 15 miles per second ; Castor, 40 to 45 miles per 

 second; Regulus, 30 to 35 miles per second; 

 Arcturus, 55 miles per second ; the nebula of 

 Orion, 5 miles per second ; Alpha Lyrso, 40 to 

 50 miles per second ; Alpha Cygni is thought 

 to be approachiag the sun at the rate of 30 

 miles' per second ; and Pollux at the rate of 

 32 miles per second. Dr. Huggins treated this 

 interesting subject very fully, in a paper read 

 before the Royal Society in June last. He 

 thus sums up generally : 



In the calculation of the estimated velocities, the 

 wave-lengths employed are those given by Angstrom 

 in his "Kecherches sur le Spectre solaire" (Upsal, 

 1868). The velocity of light was taken at 185,000 

 miles per second. 



The velocities of approach and of recession which 

 have been assigned to the stars in this paper repre- 

 sent the whole of the motion in the line of sight which 

 exists between them and the sun. As we know that . 

 the sun is moving in space, a certain part of these 

 observed velocities must be due to the solar motion. 

 I have not attempted to make this correction, because, 

 though the direction of the sun's motion seems to be 

 satisfactorily ascertained, any estimate that can be 

 made at present, of the actual velocity with which he 

 is advancing, must rest upon suppositions, more or 

 less arbitrary, of the average distance of stars of dif- 

 ferent magnitudes. It seems not improbable that 

 this part of the stars' motions may be larger than 

 would result from Otto Struve's calculations, which 

 give, on the supposition that the average parallax of 

 a star of the first magnitude is equal to 0".209, a ve- 

 locity but little greater than one-fourth of the earth's 

 annual motion in its orbit. 



It will be observed that, speaking generally, the 

 stars which the spectroscope shows to be moving 

 from the earth (Sirius. Betelgeux, Kigel, Procyon) 

 are situated in a part of the heavens opposite to Her- 

 cules^ toward which the sun is advancing ; while the 

 stars in the neighborhood of this region, as Arcturus, 

 V ega, Alpha Cygni, show a motion of approach. There 

 are, in the stars already observed, exceptions to this 

 general statement ; and there are some other consid- 

 erations which appear to show that the sun's motion 

 m space is not the only, or even in all cases, as it may 

 be found, the chief cause of the observed proper mo- 

 tions of the stars. 



