278 Transactions of the American Institute. 



In 1852, nine years after Seliwabe's discovery Prof. "Wolf of Berne, 

 was led by careful study of tlie observations, in connection with 

 ancient records, to a modification in the length of the period, which 

 is now fixed at about eleven and one-ninth years. He also succeeded 

 in proving that this period answered also to the variations in terres- 

 trial magnetism better than that of ten and one-half years previously 

 found by Lament in Munich. Thus it became evident that the inter- 

 val at which the phenomena periodically repeat themselves is the same 

 for solar spots and for variations in the direction of the magnetic 

 needle, or at least that an}' difierence in the length of the periods is 

 too small to be detected, and it is but natural that so remarkable a 

 coincidence should suggest an identity of cause. Whether this is 

 really so or not, we have no other evidence to decide. 



Geanulae Surface or the Sun. 

 About the year 1863, Mr. Xasmyth announced the discovery that 

 with a powei'ful telescope of sharp defining power, and under favor- 

 able atmospheric conditions, the whole luminous surface of the sun 

 appeared to consist of a thin layer of bright filaments shaped like 

 willow leaves, averaging about 1,000 miles in length and 100 in 

 breadth; that these lay scattered over the sun generally in every 

 variety of direction, across each other, and that the black points were 

 simply the interstices between these willow leaf filaments. This 

 announcement stimulated at once to very minute scrutiny of the face 

 of the sun, and to an active controvei'sy among the observei-s. All 

 agreed that the luminous surface was composed of bright particles, 

 but Nasmyth's description found but httle confirmation. One 

 observer proposed the term rice grains, as better representing the 

 form of the objects in question, and another compared them to gravel 

 on the beach, and a third preferred the word granulations. The facts 

 established have been very clearly set forth by Mr. Iluggins of London. 

 The granules are of various sizes, but may on the average be roughly 

 taken as about \^'' in length and V in breadth, corresponding to about 

 675 by 450 miles. Some are nearly round, others oval, and others 

 still almost without symmetry of outline. The coai-ser mottling of the 

 solar disc arises chiefiy from the alternation of lines or groups of closely 

 aggregated granules and of regions in which they are less abundant. 

 The points are the interstices between them, as they appear through a 

 telescope of insuSicient power. Mr. Huggins sums up most admira- 

 bly by saying : " The phenomenon would be well represented if we 



