Through Magic Glasses and Other Lectures

little book-I can see it now as though it were yesterday-a small square green book called World without End, which had upon the cover a little gilt picture of a stile with trees on each side

imagined myself reaching onwards and onwards beyond that stile and never, never resting. At last I consulted my greatest friend, an old man who did the weeding in my father's garden, and whom I believed to be very wise. He looked at first almost as bewildered as I was, but at last light dawned upon him. "I tell

history of those countless suns of which we see ever more and more as we increase the power of our telescopes, or catch the faint beams of those we cannot see and make them print their image on the photographic plate. And, as I grew oppressed a

, draws up the moisture from the ground to return in refreshing rain, ripens our harvests, awakens the seeds and sleeping plants into vigorous growth, and in a word sustains all the energy and life upon our earth. Yet even this star, which is more than a

his white beams of light are composed of countless coloured rays which we can separate in a prism. Now let us pass on to the more dif

u may detect a few dark spots. Then if you take your hand telescopes, which I have shaded by putting a piece of smoked glass inside the eye-piece, you will find that this shining disc is really a round globe, and moreover, although

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rojected on a she

ass. ep, Eye-piece. S, Screen shutting

of my portable telescope full upon the sun's face, and bringing a large piece of cardboard on an easel near to the other end, draw it slowly backward till the eye-piece forms a clear shar

ich are upon it, and we have brought, as it were, into our room that great g

tube where the rays of light form a real image of the object at which the telescope is pointed (see p. 44). Now an astronomer who wishes to take a photograph of the sun takes away the eye-piece of his telescope and puts a photographic plate in the tube exactly at the place wher

this strip a very fine slit is cut. Before he begins, he draws the metal up so that the slit is outside the tube and the solid portion within, and he fastens it in this position by a thread drawn through and tied to a bar outside. Then he turns his telescope on the sun, a

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ken by Mr. Selwyn, October 1860, show

called facul?, or torches, which often appear in any region where a spot is forming, while the whole face of the sun appears mottled with bright and darker spaces intermixed. Those of you who have the telescopes

e of this disc-a brilliant white halo, called the crown or corona, is seen to extend for many thousands of miles all round the darkened globe. It varies very much in shape, sometimes forming a kind of irregular square, sometimes a circle with off-shoots, as in Fig. 47, which shows what Major Tennant saw in India during the total eclipse of Aug

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t Guntoor in India, August 18, 1868, showing corona a

l sun are of a bright red colour, and they take on all manners of strange shapes, sometimes looking like ranges of fiery hills, sometimes like gigantic spikes and scimitars, sometimes even like branching fiery trees. They were called prominences before their nature was well understood, and will probably always keep that name. It would be far better, however, if some other name such as "glowing clouds" or "red jets" could be used, for there is now no doubt that they are jets of gases, chiefly hydrogen, constantly playing ove

light, a kind of pearly glow seen after sunset or before sunrise extending far beyond the region of the

ging monster of light and heat which shines down upon us? You must give me all your atte

put to receive it (see Fig. 21, p. 52). Now when the light we examine comes from a glowing solid, like white-hot iron, or a glowing liquid, or a gas under such enormous pressure that it behaves like a liquid, then the images of the slit always overlap each other, so that we see a continuous unbroken band of colour. However much you spread out the light you can never break up or separate the spectrum in any part.[2] But when you send the light, of a glowing gas such as hydrogen through th

at

OF S

the bright yellow double-line of sodium (No. 3, Plate I.) start into view across the faint continuous spectrum given by the spirit-flame. Next I will show you glowing hydrogen. I have here a glass tube containing hydrogen, so arranged that by connecting two wires fastened t

even billions of miles away. You would never mistake the lines of hydrogen for the line of sodium, but when looking at a neb

ou have a bright-coloured band you have also some dark lines crossing it (No. 2, Plate I.) It is those dark lines which enable us to guess what is going on in the sun before the light comes to us. In 1859 Pr

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nt, explaining the d

it to a focus on the prism p. sp, Continuous spectrum thrown on the wall. B, The same light, with the

of this I put a lens l, and in front of this again the prism p. The slit and the prism act exactly like your spectroscopes, and you can all see the continuous spectrum on the screen (sp, A, Fig. 48). Next I put a lighted lamp of very weak spirit in front of the slit, and find that it makes no difference, for whatever light it gives only strengthens the spectrum. But now notice

gy in heating up those waves to their own temperature, and while all the other coloured rays travelled on and reached the screen, these waves were stopped or absorbed on the way, and consequently there was a blank, black space in the spectrum where they should have been. If I could put a hyd

somewhere between the sun and us, and it must be in the sun itself, for when we examine other stars we often find dark lines in their spectrum different from t

ull of invisible water vapour, and these we easily detect, because they show more distinctly when the

lowing gases burnt here on earth. In the spectrum of glowing iron vapour 460 lines are found to agree with dark lines in the sun-spectrum, and other gases have nearly as many. Still, though thousands

ll very hot vapours, which form a kind of shell of luminous clouds around it, and in this shell, or reversing layer-as it is often called, because it turns light to darkness-we have proved tha

er in India during that same eclipse of August 1868 which is shown in our diagram (Fig. 47). Making use of the time during which the prominences were seen, they turned the telescope upon them with a sp

in full sunlight. This was done in a very simple way, when once it was discovered to be possible, and thoug

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the telescope for the exami

Collimator or tube carrying the slit at the end nearest the telescope, and a lens at the other end to render the rays parallel. c, Plate on which the prisms are fixed. e, Sm

as to stand precisely at the principal focus of the lens where the sun's image is formed (see i, i, p. 44). This comes to exactly the same thing as if we could put the slit close against the face of the sun, so as to show only the small strip which it covers, and by moving it to one part or another of the image we can see any point that we wish

the telescope forms an image of the red flame in front of the slit, though the glowing gas and the sunlight both send rays into the spectroscope, you have only to use enough prisms and arrange them in such a way that the sunlight is dispersed into a very long faint spectrum, and then the bright lines of the flames will stand out bright and clear. Of course only a small part of the long spectrum can be seen at once, and the lines must be studied separately. On the other hand, if you want to compare

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nes of pr

rum with

osphere, or light-giving mass, of the sun. This layer of luminous gases is called the chromosphere, or coloured sphere. It lies between the pho

eruptions occur these often surge up and mingle with the purer gas above. At other times the eruptions below fling the red flames aloft with marvellous force, as when Professor Young saw a long low-lying cloud of hydrogen, 100,000 miles

lit is so narrow. But when once the sunlight was dispersed so as no longer to interfere, Dr. Huggins found that it is possible to open the slit wide enough to take in the image of the whole flame, and then, by turning the spectroscope so as to bring one of the bright hydrogen lines into view, the actual shape of the prominence is seen, only it will look a different colour, either red, greenish-blue, or indigo-blue, according to the line chosen. As

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Mr. Lockyer during the tota

ctually penetrate into the secrets of the sun by bringing its image into their observatory, as we brought it to-day on the card-board, and then making it tell its own tale through the prisms o

it is partly made up of self-luminous gases whose bright lines we can see, especially an unknown green ray; while it also shines partly by reflected light from the sun, for

umber and size. In some years the sun's face is quite free from them, at others there are so many that they form two wide belts on each side of the sun's equator, with a clear space of about six degrees between. No spots ever appear near the p

between them, the edge and the spot are one, as the last trace of the dark blotch passes out of sight. In fact, it is not the spot which has crossed the sun's face, but the sun itself which has turned, like our earth, upon its axis, carrying the spot round with it. As some spots remain long enough to reappear, after about twelve or thirteen days, on the opposite edge, and even pass round two or three times, astronomers ca

, you will see that after it passes the middle of the face, the hole appears narrower and narrower till it disappears, and if you observe carefully you will note that the dark centre is the first thing you lose sight of, while the edges of the cup are still seen, till just before the spot disappears altogether. But now I will stick a wafer on, and a pea half into, the dough, marking the centre of each with ink. Then I turn the ball again. This time you lose sight of the foremost edge first, and the dar

pearing and disappearing with bright streaks or facul? round their edge, till one grows bigger than the rest, and forms a large dark nucleus, round which, after a time, a half-shadow or penumbra is seen and we have a sun-spot complet

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un-spot.

some of them tongues of fire appear to leap up from below (Fig. 53). Such spots change quickly from day to day, even if they remain for a long time, until at last by degrees the dark centres become less distinct, the half-shadows disappear, leaving only the bright

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s sun-spot.

en from time to time, whether suddenly or steadily, great upheavals and eruptions take place, bright flames

, where the down current was the strongest, would appear black even though some light would pass through. This is the best explanation we have as yet of the formation of a sun-spot, and many facts shown in the spectroscope help to

. The outburst began at eight minutes past eleven in the forenoon, and in five minutes it was gone again, but in that time it had swept across a space of 35,000 miles on the sun! Now both before and after this violent outburst took place a magnetic storm raged all round the earth, brilliant auroras were seen in all parts of the world, sparks flashed from the telegraph wires, and the telegraphic signalmen at Washington and Philadelphia received severe electric sh

to our brilliant star as he carries us along with him through space. It is only when an unusual outburst occurs, such as I have just described, that we feel how every thrill which passes through our atmosphere, through the life-current of every plant, and through the fibre and nerve of every animal has some relation to the huge source of light, heat, electricity, and magnetism at which we are now gazi

d of Science

dymium, form an exception to this

de the tube. The object-glass end is covered by two pieces of metal, which slide bac