ASTRONOMY. 



[SOLAR SPOTS. 



firmed by Galileo. The inclination of the iolar c., 

 M plain- >{ tlio elliptic was determined by Scl. 

 to be seven degrees. 



It has been remarked that the |">ts are confined to a 

 certain equatorial xotie, and tint they rarely, if at all, 



1 beyond it. Tlu-ir di^xiaition in thin respe. 

 be avail from the accompanying diagram. By Galileo 



were seen ai far a.- t us- IB- 



degrees of latitude nurth ami 

 ner extended 



thia to a soue of GO degree* 

 in breadth, called by him tlio 

 ruytii tone. They navo fro. 

 ly been men, howevor, 

 e\cn beyond thia limit, Mes- 

 sier baring teen one of 311 

 decrees, and Meelmiu one of 

 4"; <legrees of north latitude ; 

 whilst another observer has 

 detected one of CO degrees 

 of latitude. This, however, may have been one of the 

 dark font, as Herachel calls them, with which the 

 whole surface of the sun is dotted, and tend to pro- 

 duce that mottled appearance which he compared to the 

 skin of an orange. The rarity of the spots seen beyond 

 30 degrees of latitude quite confirm tlio limited nature 

 of the equatorial zone, which the multitude of spots con- 

 stantly seen on the sun renders more remarkable. It 

 was surmised by Cassini that more spots were seen in the 

 southern than in the northern hemisphere of the sun ; 

 but there does not appear to be any foundation for this, 

 as they are generally equally disposed on each side of the 

 equator. (See Fig. 19). 



In the large dark spots, or macubt, properly so called, 

 it has constantly been noticed, that the very dark central 

 portion, termed the nucleus, is fringed and surrounded on 

 Fig. 20. all sides with a shade of less intensity (Pig. 20), 



I known by the name of the penumbra (pene- 

 unilira), and which is nearly of the same degree 

 of darkness throughout. Hersohel found that 

 even the largest of these spots commenced with 

 one of these minute dark points, or pores, in the 

 bright surface of the sun, which became larger and 

 larger by degrees. When two spots were within a short 

 distance of each other, they appeared to have a tendency 

 to unite, and continued to expand until the moment of 

 reunion. When the nucleus of a spot was going to dis- 

 appear, it was noticed by Scheiner that the penumbra 

 encroached gradually, but irregularly, upon it, so that 

 the nucleus vanished before the penumbra. In modern 

 times, and with better instruments, this breaking-up of 

 a spot in the manner here specified, has been repeatedly 

 .I ; the interior edge of the penumbra becomes 

 ragged and irregular, the nucleus breaking up irregu- 

 larly, and separating into many distinct nuclei, and pre- 

 senting the appearance as if the luminous matter of the 

 sun flowed in upon the dark spot. The exterior edges of 

 the penumbra, although taking all shapes, are most fre- 

 quently rounded off, and seldom appear with sharp pro- 

 jecting promontories. This, however, is not always the 

 cane, u was believed by Scheiner, since Herschel, on one 

 or two occasions, perceived some prominent branches in 

 the nucleus, which were equally apparent in the pe- 

 numbra. Whilst observing it with his usual attention, 

 he perceived six, branches suddenly appear instead of tin- 

 two at first observed, whilst a corresponding change took 

 place in the penumbra. The same cause, therefore, may 

 be regarded as having affected both equally. In regard 

 to the proportional dimensions of nucleus, and penumbra, 

 it is generally noticed that the Utter is about throe times 

 the breadth of the former. It sometimes, though very 

 rarely, happens, that even large nuclei are unaccompanied 

 with any penumbra, and this was confirmed by Herschel 

 on one or two occasions. A huge path of penumbra was, 

 on another occasion, perceived by him without any 

 nucleu*. It U but rarely that these phenomena take 

 place in large spots ; the smaller ones, on the contrary, 

 seldom have any penumbra about them. Occasionally, 

 the spot coven such a large space on the surface of the sun, 



Fig. 20. 



(I. 



that when, by vlrtiii; of the rotation, it com<>s near tlio 

 edges, and is about to disappear, behind t 

 a dark noU-h on its limb. This was seen in IT 1 '-. 171'.', 

 1800, and JSlti. It has been dot. rmim-d l.y II. ::>.;. in 

 respect to the rolativu brightness of the nucleus and 

 penumbra, that tin- former may be estimated at 7, and 

 the latter at 4CD ; thu intensity of the solar light being 

 1000. Many observers have noticed tint tin- iir 

 edge of thu penumbra, or that immediately contiguous 

 to the nucleus, is sometimes fainter than the extvnur 

 portion. At times, this is so apparent, that thu nucleus 

 appears quite detached from the penumbra, which has 

 the appearance of a separate aunulua. In many < 

 larly round ni>ots, the |ienumbra has been noticed to 

 take a decidedly radiating appearance, like the iris of the 

 eye, and the nucleus itself observed to be riddled with 

 minute pores, presenting the appearance of wire gauze. 

 Mr. Dawes has made still further observations on the 

 telescopic appearance of the spots, and by means of eye- 

 pieces, having a very small field of view, by which he geta 

 rid of the surrounding glare of the sun's light, he has 

 detected, within the part generally called the nucleus, a 

 smaller spot, which may be considered as the nu 

 proper. From his observations it would appear as if 

 what has been termed the nucleus and penumbra, had a 

 rotary motion around the nucleus power. 



Figs. 21, 22, 23, are representations of spots really 

 seen on the sun's disc, and it will be perceived under 

 what irregular forms they appear. The long train of 

 spots represent it as much broken up, with the nuclei 

 and penumbra intermingled, and it is in this manner 

 they are noticed when about to disappear. In Fig. 21, a 

 bright streak of the surface of the sun is perceived in 

 the central part. The spots are very capricious in their 

 appearance, being sometimes very plentiful ; and at oilier 

 times the disc of the siui is entirely free from the sliu ! 

 trace. Schroeter has recorded 81 separate spots perceived 

 on the sun's disc at the same moment. For many years 

 together no spot of any considerable size has been seen. 

 Their dimensions, as already noticed, are frequently very 

 considerable ; and Schroeter saw one whose superficial 

 Hie. 21. Fig. 22. 



extent was sixteen times fjreater than that of the earth 

 tig. ?S. 



It does not appear that the great number or size of the 



