Proctor'* Astronomical I/ectures. 



THE SOLAR CORONA. 



I pass on to another object, the solar corona, which 

 gives us further indication of the force acting out- 

 ward from the sun. I have a third of those ingenious 

 experiments by Prof. Morton to illustrate these vari- 

 ous phenomena. We shall have the natural progress 

 of a solar eclipse. The inoon'3 dark body will pass 

 over the snn's disk. In America the moon is allowed 

 to travel faster than under ordinary circumstances, 

 and an eclipse which usually takes about three 

 hours will here take but a minute. [Laughter.] 

 You will notice the formation of Bailey's beads, and 

 see that the bright edge of light is broken up. Then 

 instantly bursts out the corona. I am told that this 

 jrcally corresponds very closely indeed to what is 

 Been during a total eclipse of the sun. Now what is 

 that corona ? It was once thought to be merely due 

 to the sun's light shining through our atmosphere. 

 When it was found that the prominences of hydro- 

 gen exist at a very low pressure, it 

 was a natural conclusion that there cannot 

 be a solar atmosphere extending to the hight 

 of this corona. The pressure at the Dase would be 

 enormously great. As time went on. it was seen that 

 it must be a solar appendage. In the first place, we 

 will have a picture taken by a noted French as- 

 tronomer. It is a very remarkable view, so much so 

 that considerable doubt was expressed; but that has 

 now been all removed. In the eclipse of 1868 this 

 question of the corona naturally came into great 

 prominence. Now it was to be dealt with. The 

 point was that pictures should be taken of it very 

 carefully indeed. In 1809, a picture was taken of it 

 by Mr. Gilmau of New-York, which showed a new 

 appearance an appearance of radiation, as if it was 

 combed out. You will notice all these streaks 

 spreading out. Here is a picture of the same on a 

 larger scale. In this I shall invite you to notice the 

 number of minute bright specks. Mr. Gilmau says 

 they were there as distinct entities. Zolluer has no- 

 ticed such bright specks constantly flashing out. 

 They seem to be masses of incandescent, exceed- 

 ingly bright matter. Now we begin to see that the 

 corona gives evidence of a force going out of the 

 sun. It seems to me that the evidence of such a 

 force is to be found in photographic pictures. If we 

 can show that during the progress of an eclipse the 

 moon's dark body traverses the corona, it must be 

 material belonging to the sun. We will have apicture 

 showing the corona of 1870. It was photographed 

 in Syracuse. So the doubt began to be re- 

 moved that it is really a solar phenomenon, radi- 

 ating in this wonderful way. Upon the confirming 

 evidences and features here presented, not in a pic- 

 ture subject to artistic fancies, but from the corona 

 itself, you begin to realize that there is continuous 

 action outward from the sun, and that there are 



means by which thig corona, extending a million, 

 miles from the sun, is repelled by some central forces. 

 They do not seem to be constant, for in other pic- 

 tures, taken in the eclipse of 1871, the corona was 

 very much unlike this. This picture shows tho 

 corona photographed in India by Lord Lindsay's 

 party. During the time of the eclipse six photo- 

 graphs were taken. By combining these pictures, 

 instead of that radiation there are various curves of 

 double curvature, as we call it. This will show that 

 from the center of the sun a force is produced out- 

 ward, and then there is a drawing back until a new 

 force is exerted and there is another throwing out. 

 So that there seems clear evidence that the corona 

 belongs to the sun, and that it is acted upon by a 

 propulsive force. 



THE EXHAUSTION OF SOLAR HEAT. 



Here, then, we have an immense mass of matter, 

 glowing with an enormous intensity of heat, sur- 

 rounded by vast flames, swept by storms of a nature 

 we cannot conceive, surrounded by the glowing coro- 

 na.which spreads out again into another phenomenon, 

 the zodiacal light, growing more and more tenuous, 

 and extending even as far as the orbit of Mars if not to 

 the end of the solar system. The sun seems to us to 

 be perfectly still. When we consider what we have 

 learned about him we know that all the forms of 

 uproar on this earth are as absolute quiet compared 

 with what is taking place on his surface. Even the 

 hideous groanings of the earthquake are surpassed 

 a million fold by the disturbances on every square 

 mile of that inflamed sea. This is no idle dream. 

 This great central machine of the solar orb, the 

 central heart, pulsates with life and will continue to 

 do so until the fuel is exhausted. How does the sun 

 maintain this fire ? Why is there no gradual loss of 

 energy ? If the sun were a mass of coal of the same 

 bulk, that coal, in the course of 5,000 years, would bo 

 entirely consumed, and the sun would be a mere 

 cinder. If the sun were a mass of water, which has 

 a quality of specific heat in its combinations by 

 which it gives out more heat in cooling by any num- 

 ber of degrees than any other matter, in the course 

 of 5,000 years it would lose 1,500 degrees Fahrenheit 

 in temperature. There are two theories of the man- 

 ner in which the sun's heat is kept up. One is by 

 the downfall of meteoric matter. The other is that 

 it is maintained by the gradual contraction of its 

 substance, the same process by which the rest of the 

 solar system was formed. In any case there is cer- 

 tainly a lime in the far future when the sun's heat 

 will be exhausted. 



There is indeed one wav in which we may imagine 

 that the perennial supply may be continued. Oar 

 sun is traveling along through space, carrying with 

 him the planets, the comets, &c., which circle 

 around him as he sweeps onward, and it may be 



