June 1, 1900.] 



KNOWLEDGE 



131 



reut the sun's outer garment into shreds and tatters and 

 the suu-spot minimum has arrived. 



It may be objected that even at a period of sun-spot 

 maximum the total area occupied by spots is very small 



wa!#-. 



:*> v.!<i*- 



Fig. 3. — Pliotograph of the Sun's Surface, showing gi-aiiule jiatterii. 



relatively to the soleir surface, and that wc .should see 

 more signs of this enormous disturbance of the photo- 

 sphere if it really existed ; but if reference is made to 

 Professor Hale's spectro-heliogi-aphs given in Know- 

 ledge for August, 1898, it will be seen at once that the 

 solar surface is vastly more disturbed than the spots 

 shown telescopically give any indication of, and, indeed, 

 that the telescopic appearance of the sun is exceedingly 

 misleading. As was to be expected, sun-spots are after 

 all only symptoms of the state of the photosphere, which 

 may or may not be in a spot-forming state, a fact which, 

 owing to the extreme interest attaching to the spots 

 themselves, one is perhaps often inclined to forget. 



Again, there is the obvious reply that the magnetic 

 curve so closely follows the sun-spot ciuve that we are 

 obliged to allow that when the magnetic cui-ve indicates 

 a maximum of magnetic disturbance the sun-spot maxi- 

 mum curve must also indicate a maximum of solar dis- 

 turbance ; but the conclusion is not necessarily true, 

 and I would urge that the electricity generated by a 

 rush of escaping steam, say, from a volcano, or from a 

 boiler, depends not on the volume of steam, nor on 

 the fierceness of the fire below, but on the friction of 

 the steam against the sides of the orifice, and that the 

 same volume of steam, if it were free to escape where 

 it would, might generate no electricity at all. The two 

 cases may not be parallel ; magnetic storms may not be 

 caused by the in-i-ush or out-rush of vapours in a gi-eat 

 sun-spot; but until we know what the cause is it would 

 not be at all safe to infer a maximum outbreak of solar 

 energy because we find a maximum magnetic disturb- 

 ance. 



Or, again, it may be said that the prominences by 

 their number and height must clearly indicate, coming 

 as they do so markedly in direct proportion to the sun- 

 spot maximum, that solar activity, the sun-spot 



maximum, and the prominence maximum arc syn- 

 chronous. 



It is agreed that the prominence maximum syn- 

 chronises with the spot maximum. I claim it as a 

 strong proof of the theory now advanced; if a common 

 gas jet is partly obstructed the llamo will shoot out 

 a suii^rising distance, and the smaller the orifice the 

 longer the jet; so when the photosphere is diffuse as 

 it is, ex hypothesi, at niinimuiu the solar llames have 

 but little altitude, when compact all the force is con- 

 centrated at the openings of the spots and vast jets of 

 flame ai-e expelled. 



There are some important consequences which will 

 follow if the foregoing explanation of the cause of 

 granule patterns bo admitted as a true one ; the ex- 

 planation, namely, that the absence or presence of 

 spots depends on the free floating of the solar granules 

 m tho vapours out of which they are formed; or, 

 on the conti-ary, on their subsiding into strata much 

 denser and nearer to tho .solar surface. The Poles will 

 never exhibit spots, for there tho photospheric matter 

 will always be too closely packed, owing to slowness of 

 rotation, for the surface to be broken through ; as 

 the churning of the jahotosphei'e, pi-oduced by a maxi- 

 mum, subsides the granules will gradvially sink down 

 again first towards the Poles where rotation is least ; 

 when the new spot cycle will again begin, and con- 

 tinuously sink towards the Equator, whither the sjjots 

 will follow. 



The question of tho irregularity of tho cloven-year 

 cycle will then bo a question as to how quickly or how 

 slowly tho granules composing the photosphere aro 

 allowed to sink down after a maximum outburst of solar 

 energy, and each sun-spot pcrioil will depend in somo 

 degree on the state in which tho photosphere was left 

 by the preceding one. 



The cause of the eleven-year cycle itself remains, of 



Fig. 4.— Artificial S.jliir granule [.alUin. 



course, still untouched, but possibly if the cause of the 

 irregularities were known we might get some hint as to 

 the direction in which to look for a solution of the main 

 problem. 



