1889.] on the Solar Surface during the Last Ten Years. 501 



still more strengthened by the number of times in which the spectral 

 lines have been found contorted in the observations of the chromo- 

 sphere. Bat, on the other hand, it may be urged, that if we reckon 

 the days without spots, we find very little change from 1880 to the 

 beginning of 1885 ; and the monthly mean area of sun-spots was 

 slightly in excess in July 1883 of what it had been in the previous 

 year ; and even as late as June 1885 we meet with days on which the 

 spotted area was larger than the mean extent for any month in 1882 

 or 1883. May it not be possible that the great comet of 1882, which 

 passed so deep within the limits of the corona, and which seems to 

 be but one of a numerous family, may have exercised some 

 disturbing influence, and been a partial cause of this prolonged 

 maximum ? 



The limits are rather wide for the periods separating maximum 

 from maximum, but there is much more steadiness in the lapse of 

 time between successive minima, and if we may judge from the 

 present rapid increase in the number of days without spots, the next 

 minimum should be fast approaching, and may not be far removed 

 from the computed epoch of Januarv 1890. Thus, against one 

 spotless day in 1884, we have 10 for 1885, 61 for 1886, 106 for 

 1887, 160 for 1888, and more than half the days that have been fit 

 for observation since the beginning of the present year. The im- 

 portant law connecting the mean latitude of sun-spots with their 

 extent of area, first published by Carrington, and afterwards so 

 vividly represented in curves by Prof. Sporer, has received a fresh 

 verification in the present cycle. In close relation to this is the 

 distribution of spots in the two hemispheres, and this can be well 

 illustrated by aid of curves and by mapping each spot in its true 

 heliographic position. Thus we find that the greater activity of the 

 southern hemisphere since 1883 is strongly marked, and there seems 

 to be very little evidence that successive spots tend to form along 

 meridians, although examples of this are not wholly wanting. A 

 general glance at spot distribution shows that an outbreak may be 

 expected on any meridian, but that at certain times spots congregate 

 more thickly in one longitude than in another. Thus in 1881 and 

 1882 the longitudes most favoured lie between 180^ and 270°, whilst 

 in 1887 more spots appeared between 0" and 90°. The preponderance 

 of southern spots in this year is very striking. 



The variability of the sun-spot area which we have been so far 

 considering, is a point of the greatest interest in solar physics, and it 

 may even become of great practical importance, if the supposed 

 connection between certain terrestrial phenomena and solar cycles is 

 once clearly established. But apart from this, the study of spots in 

 themselves, their wonderful changes, and their individual history, may 

 be highly instructive and teach us much concerning the nature of the 

 solar surface. The spots seen first in March and April 1884, and 

 which reappeared in May and June and July, furnish excellent examples 

 of the formation of companion groups, the principal spot acquiring a 



