i'K()"ii;i;ss (»!' AsrKo.xoMV loi; ism and is!»2. 7(^9 



I)at( 



Spiillril arc:!. i Spiillcl aic.i 



I'/litiro J.,ari;i'.st 

 snii. groiiii. 



1881 — Iaiinarv31 1,295 680 I 1883— Xovcniber 1 . . 



St'pteinlifr 12 2,089 017 u XoveiiibiT 10. 



1882-0<'tol.(n 2 2,480 3.234 18S4— March 2 



October 5 2. 065 I. 108 April 24 



1883— April 3 1.545 607 ApiiI30 .. 



A]>ril 10 1 2. 170 (170 1S,S5— .lamiaiv 23 . . 



.1 utie 30 ' 3, 050 2, 210 r Ecbrua'rv 5 . . 



.Iiilvll I 1.887 1,000 Fcbruar'v 13 



.hilV 20 j 1,425 1 1,264 Mav26* 



Si-ptcinlxT 17 ! 2,017' 1,263 .Iiiiie24* 



<)ct..l)iT 16 1 4,73(1 1,73:; July 18 



Octob«T2ll ' 1,0,50 1,300 lK01_X(>veiiil)cr22- 



Some of the above, those iiiaiked with an asterisk, may fairly be 

 taken as eoiitirming, tliough Avith less (lefiniteness, the conclusion 

 drawn from the correspondences between the greatest spots and tlie 

 greatest storms. But with tlie others it is not so. .S[»ots as imi)or- 

 tant have l)een seen upon tlu^ sun, and the magnets have scarcely flut- 

 tered, and storms as distinct have (^ccuired wlieii there have been only 

 few spots, and those but small. n])nn the visible disk of the sun. The 

 ta])lc is impoitaiit, therefore, not as adding to the weight of the evi- 

 dence in favor of the connection Ix^wcen sun s])ots and magnetic dis- 

 turbances, but as emphasi/ing a point which must not be forgotten. 

 Though the diurnal and annual changes of teriestrial magnetism con- 

 clusively i)rove the solar influence upon it, though the conclusion be- 

 tween the general sun-si)ot cycle and tlie general magn«^tic cyle is 

 clearly established, though even in minor irregularities the two curves 

 closely correspond, and though unusually large sun spots are answeretl 

 by unusually violent magnetic storms, we can not, as yet, ])roceed fur- 

 ther and ex])ress the magnitude or character of the magnetic disturb- 

 ances in terms of the sixitted area of the sun or of its principal groups 

 at the time of observation. The conclusion to my own mind seems lo 

 ix^ that though sun sjiots are the particular solar jihenoinenon most 

 easily observed, wc must not infer, therefore, that their nnmber and 

 extent afford the truest indication (»f the changers in the solar activity 

 which prodnc(! the ])ertMrbations we remark in our magnetic needles. 



SoIkv inoHiiHciiccs. — f'spccial attention has been gi\'cn to the pho- 

 tography of solar i»roininciiccs l»y Prof. (i. K. Hale ol' the Kenwood 

 observatory, ('hicago. and by M. Deslandics of the Paris observatory. 

 Pi(»f. Hale suggesteil two plans for the })iirpose; the lirst was to allow 

 the image of the sun to drift across the radial slit of a powerful sjiec- 

 troscope, tlie driving clock of the teles(;ope being slowed to produce the 

 drift. Hthen there were a prominence (tn the sun's limb the length ol 

 any bright line at the focus of the s))ectroscope would <letine the height 

 of the ])rominenee. ainl as the snn drifted across the slit this line would 

 continually change in length. If now the line in uscm ;'re made to pass 

 through a slir ju -t within the focus of the obser\ ing telescope of the 

 spectroscope cah 'd the ''second slit," so as to be in focus on a plate 

 beyond the slit, all that is recpnred to photograph liie piominence is to 

 uioyv the jilate slowly at light angle to the second slit, l-'icsh portions 

 of the plate are thus e.xiiosed to corres])onding ])ortions of the promi- 



