564 



SciEwee 



[Vol. IV., No. 99. 



SUN-SPOTS AND THE EARTH. 



" If diisky spots are varied on his brow, 

 A nd, streaked with red, a troubled color show; — 

 That sullen mixture shall at once declare 

 Winds, raiti, and storms, and elejnental war." 



Dryden. 



One of the most interesting questions of mod- 

 ern astronomy is whether sun-spots produce any 

 effect upon terrestrial affairs, and, if so, of what 

 nature is their influence, and how extensive ? 



It is an important question too ; for, if they really 

 do exert any thing like a commanding authority, 

 then our knowledge of the laws that regulate their 

 extent and frequency will give us a power of pre- 

 diction, in respect to coming seasons, of the 

 greatest value in all agricultural and commercial 

 operations. 



' It was ascertained long ago (first by our own 

 Henry), that as a sun-spot is darker, so also it is 



^i 



E »r*.b. 





■,?&.■:■ 



mm 





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SUN-SPOT AS SEEN JUNE 30, 1883 



cooler, than the bright surface of the sun. Ac- 

 cording to the observations of Professor Langley, 

 the black nucleus or u?nbra of a spot emits only 

 about fifty-four per cent as much heat as an equal 

 area of the normal surface ; and the penumbra, the 

 shaded fringe around the nucleus, about eighty per 

 cent. If, then, any considerable portion of the 

 solar surface were ever covered by the spots, we 

 should reasonably expect a notable falling-off in 

 the sun's light and heat, and an unmistakable effect 

 upon climates and the weather. 



It has been found, however, that, even in the 

 most extreme cases yet observed, the portion of 

 the sun's surface actually occupied by the spots is 

 relatively very small, seldom amounting to a five- 

 hundredth of the whole, and then only for a few 

 days at a time. The direct temperature effect of 



sun-spots is therefore still more minute, never 

 reaching a thousandth of the sun's whole heat. 



But while their direct effect is thus insensible, it 

 does not seem impossible, nor even improbable, 

 that the spots might be indicative of an abnormal 

 condition of things upon the sun's surface, such as 

 would seriously affect the earth's revenue of heat. 

 We might suppose, for instance, that they are 

 symptoms of a general chilling of the solar sur- 

 face, or, on the other hand, that they are caused 

 by some ebullition from beneath the surface, which 

 would, on the whole, raise the temperature instead 

 of lowering it, and so compensate, or even over- 

 balance, the effect of their darkness. 



In regard to this, it is now only possible to say 

 that the change, if any, is too slight to be detected 

 by our present means of observation. It is ear- 

 nestly to be hoped, that before long some apparatus 

 and method of observation may be devised delicate 

 enough to deal with the problem ; but at present 

 they do not exist, and no one knows with certainty 

 whether the sun's radiation is increased or dimin- 

 ished when sun-spots are most prevalent. 



A priori, then, we have no reason for expecting 

 any perceptible effect of sun-spots upon the earth's 

 conditions. But, on the other hand, it would not 

 do to assume that they have none; that a variation 

 in the sun's heat, even too small to be directly 

 measurable, may not indirectly produce very impor- 

 tant consequences by disturbing some nicely ad- 

 justed equilibrium. The gentlest touch of a child's 

 finger may depress a key, and fire a mine. It is 

 easy to imagine many ways in which an extremely 

 slight change in the temperature might occasion, if 

 it did not strictly cause, such alterations in the 

 cloudiness, or in the direction and velocity of 

 winds, as would seriously modify the climates and 

 the fertility of large regions of the earth. The 

 question is simply one of fact. 



Since, however, it has been discovered that there 

 is a somewhat regular, though unexplained, increase 

 and decrease in the number and extent of the sun- 

 spots (with a period of about eleven years), we are 

 in a position to investigate the subject statistically. 

 It is only necessary to compare the tabulated data 

 relating to the spots with those relating to tempera- 

 ture, barometric pressure, magnetic disturbance, 

 rainfall, height of water in rivers, — every thing, in 

 fact, that fluctuates in our terrestrial affairs : we 

 may even justifiably and properly include in our 

 inquiries such matters as the price of grain and 

 stocks, financial crises, and -epidemic diseases. If 

 in any case we find that in a sufficiently long run 



