146 



Dr. W. J. S. Lockyer. 



[Jan. 16, 



was a small indication of the presence of a spot centre of action in 

 latitude 19° in the former year, while next year the position of the 

 centre of action was in latitude 24°. Since this case was unique, it was 

 considered advisable not to connect these points together, but to leave 

 the centre of action in the year 1889 as an isolated point. 



The diagram (fig. 1) not only exhibits some of the types of curves 

 met with, but shows how the various centres of maximum spot-activity 

 were joined up with each other, year by year, for the period of time 

 over which the curves extend, namely, from 1879, the year following a 

 sunspot minimum, to about a sunspot maximum in 1883. 



Considering the curves relating to the sun's northern hemisphere, it 

 will be seen that in 1879, the year following a sunspot minimum, when 

 the spots were ending a cycle near the equator, two new outbreaks 

 occurred in latitudes about 20° and 30°. 



These two centres of activity moved towards the equator next year, 

 and by 1881 the former had disappeared, while the other rapidly grew 

 in intensity and reached latitude 15°. During this year a new outbreak 

 in latitude 30° made its appearance, and this in the two following 

 years had an equatorial trend. 



A somewhat similar occurrence took place in the southern 

 hemisphere, each of the centres of action moving rapidly towards the 

 equator. 



It is interesting to note the rapid growth and decay of these centres 

 of action, an example of which is shown commencing in 1879 in 

 latitude 28° in the northern hemisphere. 



Attention may particularly be drawn to the three prominent maxima 

 of the curves for the southern hemisphere in the years 1882 and 1883, 

 which indicate that at this period there were three definite centres of 

 spot action in existence. 



In order to bring within a small compass the results of the above 

 analysis for the whole period of investigation (the above-mentioned 

 forty-two curves, although drawn close together on a small scale, cover 

 a strip of paper 5 feet in length), a method was adopted similar to that 

 employed in the case of the prominence reduction.* 



In the accompanying plates the two sets of curves marked A indicate 

 for each hemisphere the changes in the positions of these centres of 

 spot activity from year to year plotted at equal intervals of a year. 

 The striped portion is deduced from Sporer's observations, and the 

 remainder from the Greenwich reductions. These lines have been 

 proportionally thickened to indicate approximately the relative amount 

 of spotted area at these centres of action, or, in other words, the heights 

 of the maxima points on the yearly curves. These curves thus indicate 

 for each year the positions, as regards latitude, of the particular zones 



* ' Boy. Soc. Proc./ vol. 71, pi. 6. 



