34 6 THE POPULAR SCIENCE MONTHLY. 



gin. This view of the origin of comets was held by the famous 

 Laplace, but Kant thought they originated in the solar system ; 

 and the terrestrial origin of meteorites was advocated by Sir Rob- 

 ert Ball and Tschermak. 



Lockyer then proceeds to discuss the probable construction of 

 the nebula?, and concludes that they are probably swarms of me- 

 teorites ; the collisions between the component meteorites produc- 

 ing the light emitted by these objects. He attempts to prove that 

 the brightest line seen in the spectra of the nebula?, " the chief 

 nebular line " as it is called, is coincident with the edge of the 

 magnesium fluting seen in the spectra of meteorites. The nebular 

 line certainly lies very near this fluting, but the spectroscopic 

 power used by Prof. Lockyer was quite insufficient to decide so 

 delicate a question. Recent observations by Dr. Huggins, with a 

 more powerful spectroscope, and by Mr. Keeler at the Lick Observ- 

 atory, with a higher power still, have, however, shown that the 

 chief nebular line in the spectrum of the great nebula in Orion, 

 and in some others, does not coincide with the edge of the magne- 

 sium fluting, but falls within the fluting, toward the blue end of 

 the spectrum. 



Classifying the stars in accordance with his theory, Lockyer 

 places some of them on the rising branch of a temperature curve, 

 and others, including our own sun, and stars with similar spectra, 

 on the descending or cooling branch of the curve. From an ex- 

 amination of the spectra he considers that the red and orange 

 stars of Secchi's third type, which includes many variable stars, 

 are increasing in temperature, while the still redder stars of the 

 fourth type, of which some are variable also, are cooling bodies, 

 and are "approaching the extinction of their light," The stars 

 showing bright lines in their spectra, he thinks, " are nothing 

 more than swarms of meteorites, a little more condensed than 

 those which we know as nebula?. " He identifies some of the bright 

 lines visible in these stars with the lines of hot carbon, but this 

 conclusion is disputed by Dr. Huggins. 



Considering the subject of the binary or revolving double stars, 

 Lockyer considers that they are merely condensed swarms of me- 

 teorites, which had probably their origin in a single nebulous 

 mass, or a double nebulosity. He explains the phenomena of long- 

 period variable stars by supposing one swarm to revolve round 

 another in an elliptic orbit, the increase of light at maximum be- 

 ing caused by collisions between the meteorites of the swarms 

 when they clash together at the periastron. This seems a very 

 plausible hypothesis, and quite as probable, I think, as other the- 

 ories which have been advanced to explain the phenomena pre- 

 sented by these interesting and mysterious objects. Bright lines 

 have been observed by Espin in several of the most remarkable 



