BIBLIOGRAPHY OF IIERSCIIEl's AVRITINGS. 593 



Herschcl, "W.: Synopsis of the WpariNcs of— Continued. 

 A. D. Vol. p. 



Ib08 98 147 Ohscrvatioiis. (By the method doscrihcd in /'/((/. rm«s., 1805, p. 53.) 

 The visible disk of the comet is a real one. 



147 Illumination of the Nucleus. The nucleus is round and of equal bright- 



ness all over its disk. Its color is a little tinged with red. 



148 Magnitude of the Nucleus. It appears larger at tirst sight than after 



looking a long while. 

 148 I put a number of globules of sealing wax at a known distance and 

 viewed them during the day, and remembered their [apparent] 

 magnitudes. The nucleus was compared with these and must have 

 been larger than 2". 47 and less than 2". 77. It was less than the disk 

 of Jujntcr's satellite III. 



150 Of the head of the Comet. [ Definition of the head. ] 



151 Of the Coma of the Comet. [Definition of the coma.] 



151 Of the tail of the Comet. 



One side of the tail is very well defined ; the other, hazy. 



152 Of the Density of the Coma and Tail of the Comet. 



I took notice of many small stars covered by the Coma and tail. 

 [The observations show that the interposition of the coma or tail 

 between a faint star and the eye, dimmed the star.] 



153 Nebulous appearance of the Comet. 



154 Besult of the foregoing Observations : 



156 The real diameter of the nucleus was 538 miles. 



156 I computed the phases of the comet (see Fig. 1 and Fig. 2, Plate lY, 



p. 162) for two dates. Both phases appear to me sufQcientlj^ defal- 

 cated to prove that the comet did not shine by reflected sun-light 

 only. 



157 If these remarks are well founded, we are authorized to conclude 



that the body of the comet on its surface is self-luminous. Its 

 light is more like starlight than moonlight. 



157 The tail and coma are sulliciently dense to obstruct the free passage of 

 starlight; they shine, not by reflection but by their own radiance. 



159 If I had met the comet in one of my sweeps as it appeared between 

 Dec. 6 and Feb. 21 I should have put it down as a nebula. Per- 

 haps my lists of nobulfe, then, contain some comets. 



159 Account of a new irrcgularitij lately perceived in the apparent Figure of 



the planet Saturn. 



160 I have ascribed the flattening of the i)olar regions to the attraction 



of the ring. In pursuing my observations I perceived a new irregu- 

 larity in the figure [of the ball] which I am perfectly sure had no 

 existence the last time I examined tlie planet. 



160 Observations [of the flattening in high latitudes] 1807, June 16, I per- 



ceived it ; it was independently drawn by my son, Johx Hkrsciiel. 



161 Dr. Wilson, late of Glasgow, sent me a drawing containing the 



same features made Avith one of my 7-foot reflectors at Hampstead. 



162 Explanation of the "illusion" by refraction of the light from the 



body of Saturn in the atmosphere of the ring. 



163 The ring has an atmosphere (see Fhil. Trans., 1790, p. 7). 



1809 99 259 Continuation of Experiments for investigatinj the Cause of coloured con- 

 centric Rings, and other Appearances of a similar Nature. By William 

 Herschel, LL. D., F. R. S. Read March 23, 1809. 



259-260 XXXV. Cylindrical Curves produce Streaks. 



261 XXXYI. Cylindrical and spherical Surfaces combined produce coloured 

 elliptical Rings. 



S. Mis. 31 38 



