^'December 1, 1897.] 



KNOWLEDGE. 



289 



able compared with the water, or the results obtained will 

 not be so good ; the lighted lamp must be adjusted under 

 the pan so that the point of the flame only reaches any 

 particular place selected. 



If the pulp has been well prepared the surface of it, 

 which should be about one and a-half inches below the 

 surface of the water, wUl present an exceedingly good like- 

 ness of the mottled face of the sun when free from spots. 

 Very soon after the lamp is lighted, immediately over the 

 point of flame, the surface will begin to rise — not always 

 evenly but at times Ln folds — and the faculs will appear 

 raised above the general level, and manifestly brighter 

 than the rest of the surface. If the lamp be now removed 

 these faculfe will remain for a considerable time, and then 

 slowly subside ; but if the heat be continued the granules 

 will part asunder, sometimes giving a small and simple 

 spot, and sometimes (if the resistance be considerable! 

 rising in great flocculent masses, leaving a great gaping 

 hole, often with umbra and penumbra complete. As the 

 heat continues other granules come up from below and 

 stream across the chasm, and either float away over the 

 face of our " sun," or remain as bright objects in the dark 

 spot. Even the bridges are frequently reproduced with 

 much fidelity. All this time thj heated current is streaming 

 up the " spot," and a curious effect, known to observers of 

 sunspots, is produced by refi action — a certain haziness 

 in the middle of the " spot " making seeing difiicult. Now, 

 if the lamp be moved a short distance to one side — say, two 

 inches — from where it stood before, the hot current will 

 still stream up through the same vent in our solar 

 envelope ; but now the current is oblique, and the umbra 

 will no longer be symmetrical with the penumbra, and 

 there is seen the well-known appearance of a spot which, 

 although looked at full face and not in profile, as 

 when travelling towards the Umb of the sun, shows the 

 ]Denumbra much wider on one side than the other. 



Now, if the lamp be removed the ascending current will 

 flag, then cease, and at times a descending current will set 

 in carrying with it a few floating granules. This descending 

 current is especially noticeable when an active spot is 

 working near it ; and sometimes in a large spot both an 

 ascending and a descendmg current may be observed at 

 difl'erent parts of the same spot. 



A spot when extinct will last a long time if undisturbed, 

 but the sides wfll gradually fold over, not filUng up from 

 below, but closing in at the upper edge, the penumbra 

 disappearing (Fig. 6). 



At times, instead of any spot appearing over the flame 

 of the lamp, there is a great upheaval, and masses of 

 flocculent matter hang over the opening, entirely concealing 

 it, whilst the heated fluid escapes at the sides. 



One very curious effect may be obtained, but not easily. 

 If the water is made of nearly the same specific gravity as 

 the flocculent matter — say, by adding salt to the water — and 

 the heat be appUed equally to aU parts underneath the 

 pan ; and if at the same time the granules are much 

 reduced in number so as to float free from one another 

 and no longer collect into masses — -the granules will now 

 form themselves into patches of a few inches area, divided 

 from one another by well-defined straight dark lanes, and 

 if carefully watched the granules will be seen advancing 

 towards each other and disappearing down the dark lanes, 

 whilst the middle of every patch is seen to consist of 

 granules rising. A most interesting and almost exact re- 

 presentation of this curious arrangement of solar granules is 

 given by Sir W.Huggins Ln Chambers' "Handbook of Astro- 

 nomy," and ia Sir Robert Ball's " Story of the Heavens." 

 One very noticeable feature in the behaviour of these 

 artificial spots is the great variety of form assumed, and 



that this variety depends almost, if not entirely, upon 

 the compactness or looseness of the granules. If too 

 compact, no spot of any size forms, but the hot flaid 

 rushes up through a small hole having neither umbra nor 

 penumbra ; if, again, the granules are very loose, still 

 no spot will form, but the hot fluid will escape from below 

 equally through many pores ; nor, again, will any spot 

 form if the heat be applied equally underneath, by inter- 

 posing, say, a sheet of iron between the flame and the pan. 

 The results arrived at seem to point to some such 

 conclusions as the following, some of which are in close 

 agreement with the best accepted theories. 



1. That spots are the result of comparatively small local 

 concentrations of solar energy In'loic the photosphere — that 

 is to say, they are not primarily caused by the down rush 

 of cooling vapours, which would not probably collect over 

 any one area, but be dispersed over the whole solar surface. 



2. That — startling paradox as it appears — a spot may be 

 both an elevation and a depression at the same time ! The 

 faculae may be seen to swell, rise, and open, appearing then 

 as a mound with a gaping hollow. One thing must be 

 borne very carefully in mind in comparing the telescopic 

 appearance with the imitation, viz., that the solar granules, 

 being self-luminous, cast no shadows to give the appear- 

 ance of an elevation. 



3. That unsymmetrical spots — i.e., spots with the umbra 

 not in the middle of the penumbra — are caused by the 

 local energy being no longer immediately beneath the 

 spot, the solar envelope having possibly travelled slower 

 than the portion below ; the original vent being still used 

 for the uprushing vapours, which now come obliquely. 



-ic. That spots can only be formed when the solar 

 granules are compact ; when widely difl'ased the remarkable 

 arrangement noticed by Dr. Huggins and others will occur. 



5. That the facula^ are upheavals of the photosphere 

 having the same origin as spots, but which may or may 

 not develop into spots. 



6. That possibly the solar envelope in not always of 

 the same depth. That at the times of minimum sunspot 

 activity, when the granules are presumably least compact, 

 it would be deepest ; and at maximum, when the granules 

 are most compact, it would be shallowest. 



7. That the reason for the curious fact of the spots 

 occurring in zones — i.e., neither at the poles nor at the 

 equator — may be attributable to the solar granules at the 

 equator being too diflused by the action of the sun's 

 rotation for spots to form, but too compact at the poles. 

 If so, after a minimum period of sunspot activity, when 

 the solar granules have been too diffused for spots to form, 

 we should expect to see them form again first as the 

 minimum is passing away where the solar rotation is less, 

 namely, in high latitudes. This agrees with observation. 



These may seem vast deductions from such small 

 premises as a tin pan and the margins of old newspapers ; 

 but let anyone try, and he wiU be agreeably astonished at 

 the wealth of information to be gleaned from the observa- 

 tion of these humble granules. 



[It will not have escaped Mr. East that, if a sunspot be 

 of the nature of a dark elevated cloud or of a dark surface 

 stain, the " notch " appearance must be continually pre- 

 sented. The "notch" would, I cannot doubt, be much 

 more frequently seen if it were carefully looked for. 



Mr. East's most interesting experiments must, of course, 

 not be pressed too far as furnishing analogies to solar 

 phenomena. If we accept the analogy, it is clear that we 

 must consider the interior of the sun, immediately below 

 the photosphere, as much less brilliant than the photo- 

 sphere. Here is the great crux of the sunspot problem : to 

 explain how this can be possible.— E. Walter Maunder ] 



