642 THE POPULAR SCIENCE MONTHLY. 



quoias, whose skeletons now lie white like other skeletons on the kills, 

 lift their tufted branches. The forest-trees fall in natural decay, the 

 mirror waters sleep in peace, while the centuries of the early Tertiary 

 come and go. 



FACUL^E AND SUN-SPOTS. 



By HENEY A. SMITH. 



THE sun when examined with a suitable telescope, properly adjusted 

 as to the power used, exhibits, scattered over its disk, great facu- 

 lar waves, which are elevated portions of its surface, and are composed 

 of luminous matter which has extended through its denser atmo- 

 sphere. In order that these waves may be seen, it is requisite that 

 they attain a height of at least forty-five times that of the Himalayas. 

 Their appearance is very rare in polar regions, but very abundant in 

 the close neighborhood of spots ; in fact, they generally precede the 

 formation of a spot. The faculse, at a distance from the spots, change 

 somewhat slowly, remaining for several days without much variation 

 in their appearance. But it is quite otherwise near a spot, for here 

 these waves change with a rapidity which renders it exceedingly diffi- 

 cult to make a draft of them. Movements not less than one thou- 

 sand miles in an hour are not uncommon. The faculae are generally 

 round, though sometimes they appear in long strips of light. When 

 they take the shape of a wreath, a group of spots quite soon appears, 

 as a rule. With the discovery of solar spots may be said to have com- 

 menced our knowledge of the physical condition of the sun. Kepler 

 was of the opinion that, in lines 441 and 454 of Virgil's first " Geor- 

 gic," the solar spots were referred to. We also find in the annals of 

 the Chinese, made many centuries ago, that spots were observed by 

 the unaided eye, and in the year 807 an exceedingly large spot was 

 seen for eight days. A solar spot consists, in the main, of two parts 

 the central part, called the umbra, surrounded by a less dark portion 

 called the penumbra ; and, as Professor Young has said, " The ap- 

 pearance is as if the umbra were a hole, and the penumbra filaments 

 overhung and partly shaded it from our view, like bushes at the mouth 

 of a cavern " ; the umbra being a depression below the photosphere, 

 filled with less luminous matter, while the penumbra may be seen 

 around the edges. 



It is observed that the spot, when half through its existence, is cir- 

 cular in shape, but, as it approaches disruption, it is subject to great 

 change, sudden and violent. Respecting the average life of a spot, we 

 may say it is from two to three months. The spot, however, observed 

 in 1840 and 1841 lasted eighteen months, the longest time on record. 

 Again, some may last but a few hours, being suddenly formed and 



