Nov. 24. 1882.1 



KNOWLEDGE 



419 



they would thus have learned what proportion 6 a is of the 

 whole diameter S S' of the sun, they would know how many 

 miles there are in that diameter. Suppose, for instance, 

 they found, on comparing notes, that 6 o is about the forty- 

 seventh part of the whole diameter, they would know that 

 the diameter of the sun is about 47 times 18,000 miles, or 

 about 846,000 miles. 



Now, finding the real size of an object like the sun, 

 wlio.se apparent size we can so easily measure, is the same 

 thing as finding his distance. Any one can tell how many 

 times its own diameter the sun is removed from us. Take 

 a circular disc an inch in diameter — a halfpenny, for in- 

 stance — and see how far away it must be placed to e.xactly 

 hide the sun. The distance will be found to be rather more 

 than 107 in., so that the sun, like the halfpenny which 

 hides his face, must be rather more than 107 times his own 

 diameter from us. But 107 times 846,000 miles amounts 

 to 90,-522,000 miles. This, therefore, if the imagined 

 observations were correctly made, would be the sun's 

 distance. 



(To be continued.) 



THE GREAT SUN-SPOT. 



TT7E have endeavoured (but, as we write, we are by no 

 W means sure we are in time) to give a telescopic 

 view of the aspect of the sun with the great spot on it, 

 •which has been visible to the naked eye during the last 



■week, whenever the sun's disc has been somewhat dimmed 

 by fog or mist. The actual area of disturbance is almost as 

 large as any single area ever recorded ; though no actual 

 umbra of any very extraordinary size is now visible on 

 the sun's fac& As will be seen from our picture, the 

 spot — regarding as one the whole penumbral region— has 

 four large umbr-T? and many smaller ones. We show 

 the spot as it appeared on Monday, seen under very 

 unfavourable atmospheric conditions, our rough sketch 

 being only just finished before the sky clouded over, and 

 the opportunity for further observation was lost. The evi- 

 dence of disturbance around the spot region was marked. 

 But the faculx- around the triple spot which has recently 



come into view near the eastern edge are even more con- 

 spicuous than those around the great region of disturbance, 

 though, within the large penumbral region of disturbance, 

 facular streaks of great splendour can be seen. 



We are inclined to believe that the great spot is a phe 

 independent of the great comet as 



nomenon 



no means so 



some of the daily papers have confidently asserted it to be. 

 Professor Kirkwood's theory of the association of a great 

 solar disturbance with meteoric matter following in the 

 train of the great comet of 1843 will here occur to many 

 readers. We shall touch on this later. 



THE AURORA. 



Ox Friday evening, at about the time of sunset, if not 

 earlier, a magnificent aurora was visible. When it 

 began, the sky was partly clouded, and the appearance pre- 

 sented was as though behind the darker cumulus clouds 

 there was a bank of cirrus clouds still illuminated by the 

 setting sun. But the position of the region of greatest 

 splendour, in the magnetic meridian, or some seventeen 

 degrees west of north, indicated the real character of the 

 phenomenon. As the clouds broke up and thinned they 

 presented a singular appearance, looking almost green by 

 contrast with the crimson red of the auroral clouds. When 

 they had entirely cleared away, the crimson effulgence 

 remained, though by this time it seemed somewhat less 

 intense ; it reached in streamers to a great distance from 

 the arch of greatest splendour, and for a long time the 

 crimson light could be seen extending to, and even beyond, 

 the zenith. The aurora remained, with varying brilliancy, 

 till near .5 a.m. Saturday. 



At about five minutes past six a singular phenomenon 

 was observed. A cloud of whitish light, shaped like tor- 

 pedo, passed from the south-eastern to the north-western 

 horizon (some accounts say from east to west, but the true 

 direction was from a little east of south-east to a little 

 north of north-west). It was of nearly uniform brightness. 

 Its length was nearly ninety degrees. (One observer s.iys 

 that its size, compared with that of the moon (which was 

 shining brightly at the time), was as a herring compared 

 with a sixpenny-piece ; but as he does not name the price 

 of his illustrative herring, the illustration is not so satis- 

 factory as could be wished : does he mean a penny 

 herring, or one of those which may be obtained, we under- 

 stand, at two a penny 1) It passed across the heavens in 

 about two minutes. It is described as a cometary body ; 

 but as it moved almost exactly at right-anglos to the mag- 

 netic meridian, there can be very little doubt it was an 

 electrical phenomenon. The appearance is akin to that 

 sometimes seen in high latitudes, as the auroral streamers 

 vary in position, aggregation, and length, seeming to throw 

 folds of brightness, shaped like the folds of a curtain, 

 athwart the auroral arch. 



An electrical storm of great violence prevailed from 



