BIBLIOGRAPHY OF IIERSCHEl's WRITINGS. oOS 



Herschel, W.: Syxovsis ok tui? Writings of — Continued. 

 A. D. Vol. P. 



1608 t)8 147 Ohscrvaiiom. (By tlio method described in rial. Tram., 1>(\'), ii. o3.) 

 Tlie visible disk of tlie 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 lirst 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 Jupitcr^s satellite III. 



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



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



151 Of the tail of the Comet. 



One side of the tail is very w^ell 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 Result of the foregoing Observations : 



1.56 The real diameter of the nucleus was 538 miles. 



156 I computed the phases of the comet (see Fig. 1 and Fig. 2, Plato IV, 



p. 162) for two dates. Both phases appear to me sufficiently 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 suClicieutly dense to obstruct the free passage of 

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



15'J If I had met the comet in one of my sweeps as it appeared between 

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

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



159 Account of a new irregularitij lately perceived in the ammrcnt Figure of 



the planet Saturn. 



160 I have ascribed the flattening of the polar 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 the planet. 



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



ceived it ; it was independently drawn by my son, Joux Herschel. 



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



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



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



l)ody of Saturn in the atmosphere of the ring. 



163 The ring has an atmosphere (see I'hil. Trans., 1790, p. 7). 



1«09 99 259 Contimiationof Experinients forinvestigarvng the Causeof colo,^^^^^^^^ 



centric Rings, and other Appearances of a similar ^ature. By W illiam 

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

 SSg-^O XXXV. Cylindrical Curves 2)rodMce streaks. 



261 "XXXVI. Cylindrical and spherical Surfaces combined produce coloured 

 cllijytical Rings. 

 S. Mis. 31 38 



