ASTRONOMICAL PHENOMENA AND PROGRESS. 



53 



nebular hypothesis). The revelations of the 

 spectroscope are regarded by Prof. Kirkwood 

 as especially contributing to reinstate the hy- 

 pothesis in the old degree of force. He sums 

 up the case as follows : 



1. The ring nebula in Lyra, the Dumb-bell nebula, 

 the great nebula in Orion, and others which might 

 be named, are not, as was but recently believed, ex- 

 tremely remote sidereal clusters ; but their light un- 

 doubtedly emanates from matter in a gaseous form. 



2. According to Lord Eosse and Prof. Bond the 

 brighter parts near the trapezium (in the nebula of 

 Orion) consist of clustering stars. If this be the true 

 appearance of the nebula under great telescopic 

 power, then these discrete points of light must in- 

 dicate separate and probably denser portions of the 

 gas, and that the whole nebula is to be regarded 

 rather as a system of gaseous bodies than as an un- 

 broken vaporous mass. 



3. Progressive changes in the physical condition 

 of certain nebula are clearly indicated by the fact 

 that nuclei have been established which, as shown 

 by their spectra, are not wholly gaseous, but have 

 passed, at least partially, to the solid or liquid form. 



4. The spectroscopic analysis of the light of several 

 comets reveals a constitution similar to that of the 

 gaseous nebulaa. 



The spectroscope, then, has demonstrated the pres- 

 ent existence of immense nebulous masses, such as 

 that from which Laplace supposed the solar system 

 to have been derived. It has shown, moreover, a 

 progressive change in their physical structure, in ac- 

 cordance with the views of the same astronomer. In 

 short, the evidence afforded by spectrum analysis in 

 favor of the nebular hypothesis is cumulative, and 

 of itself sufficient to give this celebrated theory a 

 high degree of probability. 



Scintillation of the Stars. A long and in- 

 teresting paper on this subject has been pub- 

 lished by Prof. L. Respighi. It gives a resume 

 of labors extending over a period of several 

 years. The instrument employed in the ob- 

 servations was a 4 inch equatorial, having a 

 direct vision prism with a cylindrical lens be- 

 tween the prism and the ocular. The phe- 

 nomena of scintillation were most distinctly 

 marked on evenings of the greatest atmos- 

 pheric humidity, and one of the deductions 

 reached by Prof. Respighi is this : that regu- 

 larity in the phenomena is a trustworthy 

 basis for predicting the continuance of the 

 weather. He says that the regularity and 

 constancy, both in direction and velocity, of 

 the motion of the spectroscopio bands with 

 respect to the meridian, namely, from red to 

 violet for stars in the west, and from violet to 

 red for those in the east, show that the scin- 

 tillation cannot be attributed to ascending or 

 descending movements of the atmospheric 

 mass, but must be due to some more general 

 cause. Finally, he advances the opinion that 

 the scintillation occurs in consequence of the 

 actual subtraction of a portion of the rays by 

 the unequal refraction of the masses of air 

 through which they are caused to pass by the 

 rotation of the earth, and he 19 thus led to 

 reject both the explanation of Arago, accord- 

 ing to which it is due to interference, and 

 that of Montigny, who ascribed it to the total 

 reflection of a portion of the ravs by strata of 

 air unequally heated. 



In the case of the planets, owing to the 

 breadth of their disks, the spectra are super- 

 posed, and the phenomena are in general not 

 distinctly seen, as they produce ordinarily 

 simple changes of brightness, or mere ir- 

 regular oscillatory movements of the images. 

 In observations upon the brighter planets, 

 however, especially Venus, when near the 

 horizon, Prof. Respighi has occasionally, nnder 

 favorable circumstances, recognized the same 

 phenomena as are displayed by the fixed stars. 



The Star Eta Argils. Mr. F. Abbott has 

 contributed a paper to the Royal Society of 

 Tasmania, mentioning further evidences of 

 changes in the star Eta Argus and its surround- 

 ing nebula. Sir William Herschel was the first 

 to note alterations in the appearances of these 

 objects. He wrote : " Gravitation still further 

 condensing and so absorbing the nebulous 

 matter, each in its immediate neighborhood 

 might ultimately become stars, and the whole 

 nebula finally take on the state of a cluster 

 of stars." Sir John Herschel, by his ob- 

 servations at the Cape of Good Hope, cor- 

 roborated this opinion, which Mr. Abbott now 

 sustains by submitting maps of his own prep- 

 aration, showing many stars not put down 

 by the Herschels. He says that the boundary 

 of the nebula is (as might be expected, if the 

 material is going into new stars) not so dis- 

 tinct as formerly and appears to be gradually 

 fading away. Mr. Le Sueur, in a report made 

 on the Melbourne reflector some time ago, ob- 

 serves that "the nebula around Eta Argus has 

 changed largely in shape since Sir J. Herschel 

 was at the Cape," and that the "star shines 

 with the light of burning hydrogen" and 

 "has consumed the nebula." Mr. Fairlie 

 McGeorge, in charge of the Melbourne tele- 

 scope, declared to the Royal Society of Vic- 

 toria, March 13, 1871, that "the object (Eta 

 Argus and the nebula) had evidently under- 

 gone great changes since Mr. Le Sueur made 

 his sketches of it. It was now beyond a doubt 

 that enormous physical changes were still tak- 

 ing place." 



Parallax of Alpha Lyra. The parallax 

 of the brilliant star Alpha Lyra> has been re- 

 cently ree"stimated with great care by Dr. 

 Brunnow, formerly director of the observatory 

 at Ann Arbor, Michigan, now Astronomer 

 Royal of Ireland. The minute star near it, 

 known as Struve's Companion, supplied the 

 means, by comparison, of making accurate 

 measurements of Alpha Lyrae. The parallax as 

 found by Brunnow is about one-fifth of a 

 second, which would make the distance of the 

 star from this planet about 93,000,000,000,000 

 of miles, or a million times farther off than the 

 sun. Profs. Peters and Struve had previously 

 estimated the parallax at from one-tenth to 

 one-fourth of a second. 



Isographio Chart of the Northern Heavens. 

 Mrl R. A. Proctor, the English astronomer, is 

 at work on an isographic chart of the northern 

 heavens, in which are to be included the 324,000 



