in connection with the Aurora of Oct 14, 1870. 79 



It will be obsen-ed, on referring to the column of " Remarks " 

 in connection with the curve, that the motion of the needle 

 coincided in its maxima and minima with the greatest activity 

 of the aurora ; and the rapid and steady easterly motion, from 

 7h 57"' -5 to 8h 5'" -5, of 42' -04, is remarkable. Viewed in the 

 declinometer it appeared exactly as though a distant disturbing 

 body was gradually receding from the magnet The flashing 

 up of brilliant streamers at the time of the beginning of this 

 easterly motion is also to be noticed. 



The magnet used in these observations is a cylindric.'il l^ar 8 

 ins. long 04 in. in diameter, attached to a plane mirror 2 ins. 

 square, and suspended by 2 ft. of untwisted silk liboi-s. Tlio 

 scale is placed 3 meters from the mirror and with tlic t(^l(sro|K> 

 deflections of 10" can be read. 



It is to be remarked that the auroral observations do urn 

 comport in accuracy with the observations of decliiiati. >u. I tax- 

 ing no assistance, I could only observe from a N. window 

 directly after having obtained the scale readings, therefore tluTc 



* with the above observation, 1 will here piv 

 an account of a systematic work in which I nm engaged and 

 which furnishes a few facts related to the subj^^ct of tlii< i.a]uM-. 



Every day about 11^ (if clear; if cloudy at the ncanst i.os>i- 

 ble time thereto) the mean penumbral diaiuerfr,* in seconds, 

 of every spot and tache on the sun is measured. Tliese diatn- 

 eters are then reduced to what they would be if viewed 

 normally. Each of these measures is then squared and their 

 sum gives a number which will vary with the umbral and 

 penumbral areas. These daily numbers are therefore directly 

 comparable quantities of the areas of solar disturbance; at 

 least so far as that disturbance is evinced in the formation of 

 spots. Similar measures are made on all the faculae I can 

 manage. Remarks are also recorded as to changes in spots and 

 faculae. In connection with the above measures the daily 

 range of magnetic declination is determined to 10". 



The object of this work is to discover, if possible, a more 

 certainly based physical connection between the daily changes 

 of area of solar disturbance and the variation of daily range of 

 declination. It seems that if the ten-year cycle of solar spots 

 has a physical connection with the varying mean yearly range 

 of declination, that such a connection can be detected and satis- 

 factorily established — if not in the special cases of ordinary 

 daily variation of declination— at least in the cases of great mag- 

 netic disturbances or " storms " either accompanied or not by au- 

 roral displays. But, as a spot indicates — if not entirely, at 



