October 4, 1894J 



NA TURE 



557 



frequency and positions (as regards latitude) of the spots may be 

 first given, a5 many references will be made to the numbers 

 therein : — 



From llie table above, it will be seen that the minimum of 1S7S 

 •was followed after 5 '2 years by a maximum in 1SS40. The mean 

 Iheliographic latitude of the spots at this j)erioit of maximum 

 decreased to 12', which i> lower than was the case at the 

 preceding maximum. Following this a minimum in iSS9"5 

 •occurred, the jjrecession of spots disappeariiiij at the mean lati- 

 tude of 7 , and a new series beginning in 1SS9 at 40° on the 

 southern hemisphere, and somewhat later at 23" and 35 on the 

 northern hemisphere. Higher latitudes were at times recorded, 

 the highest occuriing in September 1S93 and amounting to 42'. 

 The mean yearly heliographic latitude lor 1S93 diminished to 

 aS°- For the earlier part of the present year five periods of 

 rotation have given for the mean latitude also 15', indicating, 

 when compared with the two foregoing periods, a further 

 decrease in the numbers representing the "frequency." The 

 time of maximum then can apparently be placed at 1893 '5, 

 but this would most probably have to be altered if the more 

 recent observations show a further rising. 



An examination of the Carringtim observations also 

 shows this movement in the heliographic latitude. Wolf, 

 to explain it, suggested the existence of currents, which 

 •commenced with a minimum on both hemispheres in high 

 latitude?, and continued to the following minimum towards 

 lower latitudes. As imlications of these currents, it might be 

 stated that at the times of maximum suitable stiipes appear on the 

 meridian, which are for a long time free from spots and faculx. 

 This suggests that "special channels exist from time to time 

 for the hypothetical currents." 



Dr. Sporer next examines the old sun-spot observations for 

 finding out the period from the "rate" of the heliographic 

 latitudes. The cases he takes into consideration show, as lie 

 •says, "eine genu4ende Uebereinstimmung mit den neueren 

 Beobachtungen in lictrefl'des Ganges der mittleien heliograph- 

 ischen Breitc wahrend der Haufigkeits perioJen. Dagegen 



NO. I 30 I, VOL. 50"! 



scheinen nach Hem Jahre 1644 in einen Zeitraume von 

 70 Jahrcn wesentlich andere Verhiiltnisse geherrscht zu 

 haben." 



Different records, he goes on !o say. agree that from 1645-70 

 the spots observed were few. .^fter this thenumber incieased, 

 reaching an important maximum in 1716. It was even then 

 remarked (in 1715) that it was curious to note that spots were 

 visible on different pans of the solar disc at the same time. In 

 1704 and the following year, one case occurred in which spots at 

 the same time, but on two different positions of the disc, were 

 seen ; it was here expressly stated that such had not been 

 observed for sixty years. Other instances (two) of this " scarce " 

 case occurred in 1707. In 1716, spots were seen for several days, 

 in eight different places on the disc. 



Bringing together the positions of the observed spots, as re- 

 gards latitude. Dr. Sporer adds that from 1671-1713 none were 

 found in high latitudes. The highest (in 1703) was 19'. 

 I'revious tothi-, from November 1700, the latitude lay between 

 1' and 12'. At this time higher latituJes had been normal, 

 because from May 1695-Xov. 17^:0 not a single spot had been 

 obseived. For this reason Prof. Wolf is stated to have assumed 

 a minimum (iSgS'o), and determined the following minimum 

 i7i2'o, the authenticated records giving the information that 

 no spot appeared in the years 1711 and 1712. 



Some interesting facts may be stated now regarding the spots 

 on the respective northern and southern hemispheres. The 

 deficiency of spots for the former is " noch besonders hervor- 

 zuheben." In 1671, during two periods of rotation, a spot {12° 

 N. Lat. ) was observed. In 1705 and 1707 a spot is also cited 

 to have been seen, but the northern hemisphere was free from 

 them until 1713, and it was not till 1714 that they were then 

 found to be numerous ; thus one can hardly assume that, besides 

 those recorded on the northern hemisphere, more spo.s in 

 greater number appeared, for Cassini mentioned expressly, from 

 the observation of a spot from the year 1707, "the spot de- 

 ficiency of the northern hemisphere," and at the same time 

 remarked "that the constitution of the northern hemisphere 

 was different in a certain manner from that of the southern 

 hemisphere." A glance at the records for the period 1644-1670 

 also shows that in the " period of seventy years on the 

 northern hemisphere certainly no periodicity of spots had 

 occurred." 

 I The behaviour of the two hemispheres, as regarded in the 

 I light of more recent observations, is also very striking, and since 

 I 1S83 the southern hemisphere has received the greater pre- 

 ponderance of spots. This continued to be the case during the 

 minimum, and only discontinued when a rise of the number of 

 spots had begun on the two hemispheres. The year 1S91 was 

 a critical year, on account of the astonishing change that was 

 brought about. 



While on the southern hemisphere the number of spots only 

 slon-ly increased, that on the northern hemisphere attained con- 

 siderably greater proportions. The resulting ratio for the spots 

 during the year 1S91 was as 8 : 3 for the northern and southern 

 hemisphere respectively. The nature of this preponderance for 

 the northern hemisphere was not more than temporary, for in 

 1S92 it had greatly diminished, and the southern hemisphere 

 had again attained its old position. List year the proportion 

 for the northern and southern was as 7 : 10. 



The division of the spots with regard to their heliographic 

 latitude displays also ditterences fur the two hemispheres. A 

 table bringing together the results for rive periods of rotation 

 indicates a great difference in the mean values of the helio- 

 graphic latitudes; this difference, on the other hand, is to 

 a certain extent eliminated if one deals with the yearly 

 mean. 



Ueference is made also to the great change that occurs in the 

 " Rotalionswinkel " of some spots. " The most simple case for 

 such a difference of the angle of rotation teaches us, if only in 

 the first instance a spot with a penumbra is present, that a 

 division takes place, which results in the appearance of two 

 separate spots. Such spots regularly move away from one 

 another, each having a separate penumbra. The observations 

 lurnish examples which show that the distance of the spots for 

 many days continually increases, and that the angle of rotation 

 of the preceding soot is very considerably greater than that of 

 the following one." The observations included in this volume 

 contain examples of these in great number. 



W. J. L. 



