130 



KNOWLEDGE. 



[June 1, 1900. 



rise, become relatively cool, travel hither and thither 

 over the upper surface, so far as other heated masses 

 also striving equally to extend themselves will aJlow, 

 and sink again to make room for others, and rise again 



Fix. 1. — Photograph of the Sun's Surface, showing granule pattern. 



in an endless series. And to these larger masses applies 

 no doubt M. Janssen's remark as to, what he names, 

 the " I'li'raents grauulaires." 



" On sent que la sphere a ete la forme jireminre des elements, ces 

 elements sont constitues par une niatiere tres mohile qui oMe avec 

 facilite aux actions extericures." 



That is to say, the rising masses of heated photo- 

 spheric material are normally spherical, and the 

 rectilinear aiTangement forming the " reseau " is the 

 result of the mutuaJ pressure of the masses. 



An attempt has been made to reproduce these reticu- 

 lations by the artificial method previously given in 

 Knowledge, and some examples are presented in the 

 accompanying illustrations, together with two repro- 

 ductions of the Meudon photographs. The method con- 

 sists in floating granules of the curd of milk in a 

 saturated solution of salt and water, and putting the 

 pan containing the solution on a hot plate; almost 

 immediately spherical or at least round-headed masses 

 of the granules begin to rise, and when these masses 

 meet they mutually compress one another, the lines of 

 impact being mostly straight : thus we get a very regular 

 " reseau," with this remarkable piece of information that 

 the lines of separation between the areas are formed 

 exclusively by descending granules, the middle of the 

 reticulations being the area of ascending granules. Let 

 me quote again M. Janssen's description of his " reseau." 



" I'n examcn attentif des jihotograpliies montre que la surface 

 Ac la jiliotosphire n'a pas une con.stitution iiniforme dans toutes ses 

 parties, mais qu'ellc se divise en une sferie de figures plus ou moins 

 distantes^ les unes des autres, ct presentant une constitution 

 partieuliere. 



" Ces figures ont des contoui-s plus ou moins arondis, sou\ent 

 rectilignes, et rapj)elant le plus ordinairement des polygoues." 



These polygons are a very distinct feature in the 

 artificially produced " reseau photospherique." 



There is one jsoint absolutely essential to the success 

 of making the granules play in this manner — they must 

 be able to move freely in the fluid, any tendency to 

 become flocculent, or to sink to the bottom in a mass, 

 instantly stops this pattern forming; in this case spots 

 may be formed in the compacted granule masses, as 

 explained in a previous article (Knowledge, December, 

 1897), but no granule patterns will play on the 

 surface. 



Now, if these artificial granules truly represent the 

 behaviour of the solar granules, it is evident that the 

 conditions on the sun whem spots are formed are 

 exactly the opposite of those when reticulations are 

 fashioned, the former depending on the compactness, 

 and the latter on the diffusiveness of the photosf)heric 

 materials. 



Consequently, it became important to ascertain at 

 what period of sun-spot activity Sir W. Huggins' draw- 

 ing was made. Sir William very kindly informs me 

 that " the drawing was made on April 26, 1866, one 

 year before the minimum, the previous minimum of 

 1856 having been a remarkable one. The diagram 

 does not represent the actual appearance of any one 

 area of the sun's surface, but some of the more charac- 

 teristic of the modes of grouping of the bright granules." 



It seems to be always taken for granted that maximum 

 " sun-spottedness " and maximum solar activity are the 

 same thing — in fact, convertible terms. I venture to 

 submit that it may be nothing of the kind, but the 

 exact opposite may be nearer the truth : when the solar 

 energy is at its maximum the photosphere may be so 

 torn and churned and dispersed that it has not com- 

 pactness enough left for spots to be able to form, and if 





Fig. 2. — Artilicial ^!olar granule pattern. 



some few form they are small and soon obliterated. 

 M. Janssen observes: — 



" J'ai pu constater, par nos series photospherique que quand le 

 soleil est a I'epoque d'uu minimum, les taclies ont une surprenante 

 tendance .^ se dissoudre. L'annee 187(5 en presente plusieurs 

 examples remarkables." 



I would suggest that spots are a sign of reviving solar 

 fury, which does not reach its maximum \intil it has 



