July i6, 1903] 



NATURE 



257 



18600 

 I > I I 



OiV A PROBABLE RELATIONSHIP BETWEEN 

 THE SOLAR PROMINENCES AND CORONAL 



T N a previous number of this Journal (Nature, vol. Ixvii. 

 p. 569, April 16) an account was given of the results 

 which had been deduced from a minute investigation of 

 the percentage frequency of prominences as determined from 

 observations made by Secchi and Tacchini at Rome, and 

 Ricco and Mascari at Catania and Palermo. It was there 

 shown that the chief centres of prominence action, that 

 is, the zones in which the greatest percentage frequency 

 of prominences occurred, indicated movements in helio- 

 graphic latitudes, the general tendency of these being in 

 a direction towards the solar poles, and not towards the 

 equator, as is the case with the spots. Attention was 

 also directed to the fact that these centres of prominence 

 activity were not restricted to a narrow zone like the spots, 

 which only occur between the latitudes ±5° and ±35°, but 

 that at times they 

 were numerous in 

 such high latitudes 

 as ±80°, and even 

 higher. 



The present 

 article contains an 

 account of the re- 

 sults of a general 

 survey that has 

 been made regard- 

 ing the connection 

 between the 



changes of position 

 of these centres of 

 prominence action 

 and the various 

 forms of the corona 

 as observed during 

 total eclipses. 



It has been sug- 

 gested, and the idea 

 is generally ac- 

 cepted, that the 

 various forms of the 

 solar corona are 

 intimately connec- 

 ted with the varia- 

 tion in the spotted 

 area of the sun's 

 surface. Thus, 

 generally speaking, 

 at about the epochs 

 of sun-spot maxima, 

 the corona is appar- 

 ently very irregular 

 in shape, there be- 

 ing little or none of 

 the exquisite tracery 

 at the sun's poles 

 which is so evident 

 at the epochs of 

 sun-spot minima, 

 while the streamers 

 are less confined to 

 mid-solar latitudes 

 and the region near 

 minima. 



on the positions of the coronal streamers, the three different 

 types here adopted refer in the main to the positions of 

 these streamers in relation to the solar equator and poles. 



In the first, or " polar " group as it has here been called, 

 since streamers are found near the solar poles, all those 

 coronas are included which seem to have no regular form. 

 The typical features of this group are that the polar rifts 

 are absent, being replaced to a great extent by streamers 

 at, or very close to, the poles, and the streamers are 

 numerous in nearly all solar latitudes ; also there is no 

 definite equatorial extension. To this class the following 

 coronas belong, i860, 1870, 1871, 1882, 1883, and 1893. 



In the third, or " equatorial " group, since the streamers 

 are in lower latitudes, and consequently more equatorial, 

 the form of the corona is very regular. The polar rifts 

 have a great spread in latitude and are well defined, while 

 the large streamers are restricted to the regions near the 

 equator ; in fact, the great equatorial extensions are best 



STREAMERS 



POLAR 



POLAR , &^ 



(ei MvAnc-) 



EQUATORIAL 



CM WINOVANC^. 



18600 



1870-0 



1880-0 



1890-0 



1800-0 



:• —Curves showing the relationship between the different forms of the corona, the positions of the centres of action of 

 prominence phenomena and the general sun-spot curve. The continuous and broken vertical lines indicate the epoch 

 of the maxima and minima respectively of the last mentioned curve. 



the equator than they are at the 



The facts that sun-spots do not appear nearer the poles 

 than latitudes ±35°, and that large coronal streamers and 

 prominent rays are sometimes visible in much higher lati- 

 tudes than these — in fact at times near the poles of the sun, 

 and consequently outside the regions of spot activity — 

 suggested that the occurrence of prominences, very im- 

 portant factors in the mechanism of the solar atmosphere, 

 might be closely connected with them. 



In the present general inquiry, the forms of the coronas 

 that have been observed since the year 1857 have been 

 divided into three main types, and this classification, which 

 is not new, is one into which most of the coronas, with the 

 exception of two, namely 1865 and 1885, can be easily 

 placed. Since the forms of coronas are dependent chiefly 



1 Abstract of a paper recently communicated to the Royal Astronomical 

 Society by Dr. William J. S. Lockyer. 



seen in this type. This form generally takes the shape 

 of a " wind vane," and is often referred to as such. The 

 coronas which come into this category are those of 1867, 



1868, 1878, 1889 January, 1889 December, 1900 and 1901. 

 The second group of this classification may be termed 



the " intermediate " type, as the streamers are about half 

 way or intermediate between the poles and the equator. 

 In this group the polar rifts are present, but they are not 

 so extensive in latitude as in the " equatorial " class. The 

 coronal streamers also approach nearer the polar regions 

 than in the " equatorial " class, but not so close as in the 

 " polar " group, while the equatorial extensions are not 

 in such great evidence. Generally speaking, this form of 

 corona is due to a large streamer in each quadrant, which 

 gives the corona the appearance of a square, hence the 

 name "square corona," which has been often used. 

 The coronas which fall under this heading are 1858, 



1869, 1874, 1875, 1886, 1887, 1896, 1898. It may be stated 



NO. 1759, VOL. 68] 



