6 ROUGH WAYS MADE SMOOTH. 



tion was at variance with the relation between the values of 

 the apparent diameters of the sun and moon as computed 

 for the time of the eclipse by aid of the solar and lunar 

 tables. The corona, then, must have resembled that seen 

 by Clavius, and since the year 1598 must have been very 

 near the time of fewest spots, this observation accords with 

 the theory we are examining. 



The next observation is that made by Wyberd during 

 the eclipse of 1652. Here there is a difficulty arising from 

 the strange way in which the sun-spots behaved during the 

 interval from 1645 to 1679. According to M. Wolf, whose 

 investigation of the subject has been very close and search- 

 ing, there was a maximum of sun-spots in 1639 followed by 

 a minimum in 1645, the usual interval of about six years 

 having elapsed ; but there came a maximum in 1655, ten 

 years later, followed by a minimum in 1666, eleven years 

 later, so that actually twenty-one years would seem to 

 have elapsed between successive minima (1645 an( ^ 1666). 

 Then came a maximum in 1675, nine years later, and a 

 minimum in 1679, four years later. Between the maxima 

 of 1639 and 1675, including two spot periods, an interval of 

 thirty-six years elapsed. There is no other instance on 

 record, so far as I know, of so long an interval as this for 

 two spot-periods. In passing, I would notice how little this 

 circumstance accords with the theory that the sun-spots 

 follow an exact law, or that from observations of the sun, 

 means can ever be found for forming a trustworthy system 

 of weather prediction, even if we assumed (which has always 

 seemed to me a very daring assumption), that terrestrial 

 weather is directly dependent on the progress of the sun- 

 spot period. But here the irregularity of the spot changes 

 affects us only as preventing us from determining or even 

 from guessing what may have been the condition of the 

 sun's surface in the year 1652. This year followed by 

 seven years a period of minimum disturbance, and preceded 

 by three years a period of maximum disturbance ; but it 

 would be unsafe to assume that the sun's condition in 1652 



