554 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschcl, W.: Synopsis of the Writings of— Continued. 



A.D. Vol. P. 



1795 8j 51 Explanation of the luminous shelving sides of a sun-spot. The sun 



may have inequalities [like mountains] on its surface perhaps 500 



or 600 miles high. 

 53 In 1791 I observed a large spot on the sun, depressed below the level 



of its surface. 



53 An optical deception takes place now aud then when we view the 



moon, which is that all the elevated spots on its surface will seem 

 to be cavities, and vice versa. 



54 How very ill would these observations agree with the ideas of solid 



bodies bobbing up and down in a fiery liquid? with the smoke of 

 volcanoes or the scum upon an ocean ? 

 54-58 Observations in detail from 1792, Aug. 26, to 1794, Oct. 13. 

 . 54 1792, Sept. 2. Two spots on the sun were seen with the naked eye. 



55 It may not be impossible, as light is a transparent fluid, that the sun's 



real surface may also now and then be perceived, as we see the 

 shape of the wick of a candle through its flame. 



56 Faculae seem generally to accompany the spots, and they are certainly 



elevations on the surface. 



57 The sun cannot be so distinctly viewed with a small aperture and 



faint darkening glasses as with a large aperture and stronger ones. 

 57 About all the spots the shining matter seems to have been disturbed, 

 and is uneven, lumpy, and zig-zagged in an irregular manner. 



57 I call the spots black, not that they are entirely so, but to distinguish 



them. There is not one of them to-day which is not at least partly 

 covered over with whitish and unequally bright nebulosity. 



58 If the brightness of the sun is occasioned by the lucid atmosphere the 



intensity of the brightness must be less where it is depressed. 

 The results of these observations are : The sun has a very extensive 

 atmosphere, which consists of various elastic fluids more or less 

 lucid and transparent, and of which the lucid one is that which fur- 

 nishes us with light. 



59 The manner in which I suppose the lucid fluid of the sun to be gen- 



erated in its atmosphere may be better .understood from an anal- 

 ogy drawn from the generation of clouds in our own atmosphere. 

 [This analogy is stated.] 



60 That the emission of light must waste the sun is not a difficulty that 



can be opposed to our hypothesis. 



60 Many of the operations of nature are carried on in her great labora- 



tory which we cannot comprehend, but now and then we see some 

 of the tools with which she is at work. [The many telescopic com- 

 ets may restore to the sun what is lost by the emission of light.] 



61 According to my theory a dark spot in the sun is a place in its atmos- 



phere which happens to be free from luminous decompositions, and 

 faculoe are more copious mixtures of such fluids as decompose each 

 other. 



62 The penumbra which attends the spots being depressed more or less 



to about half way between the solid body of the sun and the upper 

 part of the regions where luminous decompositions take place, must 

 of course be fainter than other parts. 

 62 The regions where the luminoiis solar clouds are formed, adding thereto 

 the elevation of the faculae, cannot be less than 1,843 miles nor much 

 more than 2,765 miles. 



