On the Chemical Constitution of the Stars. 



211 



between a hydrogen and a solar star lies in the more or less effectual 

 mixing up of the constituents. If we could introduce a stirrer into 

 7 Lyras there can be no doubt whatever that the low-temperature 

 lines of iron would make their appearance, while, on the other hand, 

 if we could stop all convection currents on the surface of the sun the 

 hydrogen which now lies under the photosphere would gradually 

 diffuse out and give greater prominence to its characteristic absorp- 

 tion lines. 



In the face of the direct evidence of the absence of convection 

 currents in the hotter stars, it is not necessary for the purpose 

 of my argument to discuss why this is the case, but it can be seen 

 that diminished gravity, diminished density, and consequently 

 increased viscosity, will contribute to the effect, while effectual 

 radiation will, owing to the smaller density, take place more evenly 

 through a thicker layer of the envelope, so that the principal cause 

 of convection currents will also be much diminished. The explana- 

 tion I have given does not differ materially from that brought forward 

 by Dr. Huggins in his address as president of the British Association 

 at Swansea. I do not say that difficulties may not be raised against 

 it, bat difficulties may be raised also against the theory of dissocia- 

 tion, and there is especially one question which Professor Lockyer 

 must be prepared to answer. Amongst the heavier metals, tellurium, 

 antimony, mercury, are not represented in the sun, but they are found 

 in Aldebaran. To be consistent, we must, if we adopt the theory 

 of dissociation, assert, that these metals are decomposed in the sun. 

 But if I understand Professor Lockyer right, he believes that with our 

 strongest sparks we can exceed the state of dissociation which exists 

 in the reversing layer of the sun. Take such a strong spark then from 

 a pole of mercury, do you get lines of helium, or of calcium, or of 

 hydrogen ? This seems to me to be almost a crucial experiment, 

 Possibly, of course, we should get high-temperature lines not 

 hitherto looked for, but present in the sun. If so, the objection 

 would fall to the ground, but if this is not the case, and if mercury 

 at a high temperature refuses to be dissociated into simpler elements, 

 a most serious objection to the theory would have to be answered. 



With regard to the division of stars into those of rising and those 

 of falling temperature, some of Professor Lockyer's remarks lead me 

 to think that he has not followed the recent development of the 

 nebular theory. To him the nebular theory is still that of Kant and 

 Laplace, while Lane, Lord Kelvin, and Bitter have applied the 

 dynamical theory of heat to the treatment of gaseous masses, con- 

 tracting under their own gravitation, and have clearly shown that a 

 radiating and contracting mass is not necessarily a cooling mass ; on 

 the contrary the interior of our sun is almost certainly rising in tem- 

 perature at the present moment. Bitter's work is of great importance. 

 VOL. lxi. o 



