Curiosities of Science. 67 



SPOTS ON THE SUN. 



Sir John Herschel describes these phenomena, when watched 

 from day to day, or even from hour to hour, as appearing to en- 

 large or contract, to change their forms, and at length disappear 

 altogether, or to break out anew in parts of the surface where 

 none were before. Occasionally they break up or divide into 

 two or more. The scale on which their movements takes place 

 is immense. A single second of angular measure, as seen from 

 the earth, corresponds on the sun's disc to 461 miles ; and a 

 circle of this diameter (containing therefore nearly 167,000 

 square miles) is the least space which can be distinctly dis- 

 cerned on the sun as a visible area. Spots have been observed, 

 however, whose linear diameter has been upwards of 45,000 

 miles ; and even, if some records are to be trusted, of very much 

 greater extent. That such a spot should close up in six weeks 

 time (for they seldom last much longer), its borders must ap- 

 proach at the rate of more than 1000 miles a-day. 



The same astronomer saw at the Cape of Good Hope, on the 

 29th March 1837, a solar spot occupying an area of near five 

 square minutes, equal to 3,780,000,000 square miles. "The 

 black centre of the spot of May 25th, 1837 (not the tenth part 

 of the preceding one), would have allowed the globe of our 

 earth to drop through it, leaving a thousand miles clear of 

 .contact on all sides of that tremendous gulf." For such an 

 amount of disturbance on the sun's atmosphere, what reason 

 can be assigned ? 



The Rev. Mr. Dawes has invented a peculiar contrivance, 

 by means of which he has been enabled to scrutinise, under 

 high magnifying power, minute portions of the solar disc. He 

 places a metallic screen, pierced with a very small hole, in the 

 focus of the telescope, where the image of the sun is formed. 

 A small portion only of the image is thus allowed to pass 

 through, so that it may be examined by the eye-piece without 

 inconveniencing the observer by heat or glare. By this ar- 

 rangement, Mr. Dawes has observed peculiarities in the con- 

 stitution of the sun's surface which are discernible in no other 

 way. 



Before these observations, the dark spots seen on the sun's 

 surface were supposed to be portions of the solid body of the 

 sun, laid bare to our view by those immense fluctuations in 

 the luminous regions of its atmosphere to which it appears to 

 be subject. It now appears that these dark portions are only 

 an additional and inferior stratum of a very feebly luminous 

 or illuminated portion of the sun's atmosphere. This again in 

 its turn Mr. Dawes has frequently seen pierced with a smaller 

 and usually much more rounded aperture, which would seem 



