244 Sir Norman Lockyer and Dr. W. J. S, Lockyer. [Jan. 14, 



" The Relation between Solar Prominences and Terrestrial Mag- 

 netism." By Sir Norman Lockyer, K.C.B., F.R.S., and 

 William J. S. Lockyer, M.A., Ph.D., F.R.A.S. Received 

 January 14, — Read January 29, 1903. 



[Plates 4 axd 5.] 



It has been stated in a previous communication* that a preliminary 

 reduction of the Roman observations of prominences, observed on the 

 sun's limb by Tacchini, indicated that, in addition to main epochs of 

 maxima and minima of prominences coinciding in time with those of 

 the maxima and minima of the total spotted area, there are also 

 prominent subsidiary maxima and minima. 



One of us has pointed out in a recent communication to the 

 Academie des Sciences t that a comparison of the frequency of 

 prominences visible in each solar latitude with the frequency of the 

 most intense magnetic storms, indicated that (a) magnetic storms 

 classed as " great " by Ellis, and the greatest prominence activity near 

 the poles of the sun occurred at the same time ; and (b) that the curve 

 of general magnetic activity was nearly the same as that of the 

 prominences observed near the solar equator. 



The object of the present communication- is to give a more detailed 

 account of the research so far as it has gone. 



The Observations of Prominences. 



The fine series of observations, made by Tacchini, of the numbers 

 and latitudes of prominences seen on the sun's limb was used as a 

 basis for the curves discussed. These observations were commenced 

 in 1872, and have been continued up to the present day, so that we 

 have a valuable continuous record. They have been published! from 

 time to time in full detail, thus rendering it possible to deal with them 

 in any manner that may be desired. In the reduction of the observa- 

 tions each zone of 10° was examined and discussed by itself. The 

 observations were divided in the first instance into groups of three 

 months, and the percentage frequency of the prominences was deter- 

 mined by dividing the number observed by the number of days on 

 which observations were made in this period. 



In this way a set of eighteen curves, nine for each hemisphere, was 

 made, showing the variation from year to year of the percentage 

 frequency of prominence activity in each ten-degree zone. 



* ' Roy. Soc. Proc.,' vol. 70, p. 502. 



f « Comptes Rendus,' vol. 135, Jfo. 8, 25th August, 1902. 



J 1 Societa degli Spettroscopisti Italian!,' vol. 1, 1872; vol. 29, 1900. 



