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outburst. The cycle of changes therefore described above had 

 been completed in less than one hour. But the most astounding 

 observation of this kind ever made is that reported by Professor 

 Young on September 7, 1871. At 12-30 on this day he noticed 

 on the western limb of the sun a large cloud connected by three 

 stems to the chromosphere. Beyonds its great size, some 55,000 

 miles high and 100,000 long, there was nothing very remarkable 

 at first about this fiame. But after half an hour's interval the 

 state of affairs had entirely changed. For in the meantime it 

 had literally been blown to fragments. We quote Professor 

 Young's account : " While I was watching I saw some of the 

 filaments ascend from an elevation of 100,000 miles to one of 

 200,000 miles in ten minutes of time, with an average velocity 

 of 167 miles a second." This observation has received a very 

 careful discussion from Mr. Procter. He shows that if the 

 filaments Young observed actually started from the chromosphere 

 they must have possessed an initial velocity of more than 250 

 mUes a second. Nay, more ; it is evident from his calculations 

 that these patches of fiame must have encountered considerable 

 resistance to their upward passage through the solar atmosphere 

 between the heights of 100,000 and 200,000 mUes, and more 

 than this the intensity of the force of gravity on the sun which 

 would tend to pull them downwards is 27^ times that of the 

 same force on the earth. Taking all these facts into account, 

 the initial velocity of projection cannot be placed at a lower 

 figure than 500 miles a second. Had the particles observed been 

 sohd instead of gaseous, such a velocity of projection would have 

 been sufficient to have driven them into space never to return 

 again. So inconceivable are such velocities to the human mind, 

 that Young was tempted at fii'st to suppose that in such phen- 

 omena there was not a real transference of matter, but only a 

 lighting up of matter already in position, something analogous to 

 the explosion of a train of gunpowder. But here again the won- 

 derful spectroscope comes to our aid, and its teachings are 

 that in the velocities observed, we are dealing with real velocities 

 of incandescent particles. No doubt many of our readers have 

 noticed what happens to the note given by the whistle of a train 

 as it dashes through a railway station. As it approaches the note 

 becomes continually shriller and of a higher pitch, and the 

 opposite effect is observed as it rushes out of sight ? Why is 

 this ? Because sound is conveyed to our ears by waves in the 

 air, and the more waves that reach us in any given interval of 

 time the higher is the corresponding note, and the fewer the 

 lower. A precisely analogous effect happens in the case of a 

 body giving out light vibrations instead of sound vibrations. 

 Light is conveyed not by the air but by ether, and the length of 

 the waves is very small indeed. The unit for measuring them 



