ON SUNSrOTS AND TERRESTRIAL riFENOMENA. 



449 



ilitavy 

 icientj 

 tance, 



spots 

 by tlie 

 idnced 

 (arallel 



of the 



Even 

 IS, it is 

 that of 

 ty than 

 lown in 

 , should 

 iifferent 

 ling one 

 .1 Wolfs 



"We are 

 complete 

 in future 

 out esti- 

 lai' varia- 

 m of the 

 id the six 

 month on 

 d sunspot 

 from July 

 le measure 



tion to Its 

 movement, 



to travel 

 dcllection ■• 



living the 

 train iu thf 



f its daily 

 aviation i^ 

 ■no greatest 

 arly seven 

 ctobcv and 

 iemisphei'C 

 ,n3 there is 

 ic variation 



out almost 

 Lf the mag- 



netic declination was coincident with that of sunspot frequency, and 

 that its daily range increased and decreased witli that of the spots. 

 The increase of tlio amplitude is approximat(>ly proportional to the 

 variation at different places of the earth's surface, so that on the average 

 the daily oscillation 1;, from 1*5 to 1'7 times as large at times of sunspot 

 maxima as at ti-nes of sunspot minima. If we compare together the 

 curves of snusii'"<t freqneacy and those of the daily range, we find that not 

 only do the maxima and minima correspond with each other, but that the 

 shape of the curves is throughout very similar, the irregularities of one 

 being generally repeated in the other. The connection seems so close that 

 Wolf has attempted to represent it by means of a mathematical formula. 

 Denoting by M the daily range of declination, and by W Wolf's number 

 for sunspot frequency, the following equation is found to bold very 

 nearly: m =: a -f IjW. a and b are two constants,, which depend on 

 the place of observation. Wolf has determined them for thirty places, but 

 the question of the constancy of these factors can only be settled by 

 further observations. According to Ellis and Balfour Stewart, the curves 

 of daily declination range lag rather behind those of sunspot frequency; 

 even sudden outbursts of solar disturbance seem to bo represented in the 

 magnetic curves by an increase iu the daily range, which takes place 

 nearly simultaneously. 



The intensity of the horizontal component of the earth's magnetism 

 has a daily range, showing an o.^cillation which is larger at times of sun- 

 spot maxima than at times of sunspot minima. 



Hansteen ' has investigated the changes in the daily average of magnetic 

 declination and of dip, and has found that they present a period corre- 

 sponding to that of sunspot frequency j the horizontal intensity is larger, 

 and the dip less at times of fewer sunspots ; and these two elements vary 

 together in such a way as to suggest the probability that the vertical 

 force remains comparatively unaltered, so that the change in the dip seems 

 produced by a change in the horizontal foi-ce only. At Kew,'^ however, 

 the change in the hori:'jntal force seems inappreciable, while the dip 

 i.s increased at times of numerous sunspots, which latter result agrees 

 with tliat of the Munich observers, and seems to point to a change in the 

 vertical force. At Toronto,''^ on the other hand, both the dip and the 

 horizontal force seem to increase simultaneously with increase of sun- 

 spots, so that here the vertical force seems to alter more rapidly than the 

 horizontal component. But it must bo remembered that changes in the 

 dip and in the horizontal force cannot be determined to the same degree 

 of accuracy as change of declination, and these last-mentioned results are 

 therelbre not established with certainty. Fritz has investigated the ques- 

 tion whether the state of the sun's surface aU'e<^ts the rate at which the 

 secular change of declination takes place, and has found that at Paris, 

 Brussels, and ^Munich the secular change takes [ilaee most quickly when 

 there are many spots on the sun. The Kew results show, however, an 

 increase in declination at times of many spots, which denotes a retardation 

 in iho secular change. The increase which is given by the Toi'onto 

 measnreraeTits, on the other hand, supports the view expressed by Fritz, 

 as the declination at Toronto at the present time increases. 



p. 24. 



' Ad. Xachr. No. 10G9 (1857). 



' See the article ' Terrestrial Magnetism ' in tbo Ennjcl Brit. (Balfour Stewart), 



1884. 



00 



