SPOTS ON THE SUN". 



merely dark spots or surfaces, is shown by the fore-shortening 

 of the nearest edge as they arrive at the verge of the sun's 

 disc, and are consequently presented edgewise to the eye, so 

 that a spot may have the appearance of fig. 2 when seen in 





FIG. 2. FIG. 



front-view near the centre, and of fig. 3 when seen fore- 

 shortened near the edge of the sun's disc. These spots 

 (although but specks in comparison with the vast surface of 

 the sun) are yet of prodigious magnitude, some having been 

 calculated to measure 18,000 miles across large enough for 

 two such worlds as ours to pass through side by side ! From 

 the rapid motion of the " penumbra " or edges of these spots, 

 which alter, open, and close up very rapidly, and from some 

 of them being semi-dark, others quite dark, &c., it has been 

 concluded that the sun has at least two surrounding 

 atmospheres, that the body of the sun is not luminous, nor 

 the first atmosphere or that nearest to it, but that the outer 

 one is, and that the dusky appearance of the inner, as seen 

 through openings of the luminous outer atmosphere, results 

 from its being very strongly illuminated by the outer one ; 

 this luminosity may be (and probably is) only comparative, 

 for the spots which appear black may be yet very bright, 

 appearing black only in comparison with the extreme 

 brilliancy of the outer atmosphere, just as a bar of red-h ot 

 iron appears black when held up to the sun. The course 

 which the planets take round the sun is not exactly circular, 

 but deviating from it more or less, never being quite a 

 circle. The orbit of each planet, if accurately computed 

 and laid down on paper, proves to be that form of curved 

 line called an " ellipse," or that form which instead of having 

 one centre, as in the circle, from which all lines radiating to 

 the circumference are equal in length, has a longer and 



