BIBLIOGRAPHY OF RERSCIIEL's WRITINGS. 599 



Herschcl, V/.: Synopsis of tisk AVjutings of- Contimiod. 



A. D. Vol. p. 



1812 102 131 The shortening of Ihe Tail. 



132 Increasing Darkness between the Streams that enclose Ihe Tail. 



133 Of the real construction of the Comet, and its various Parts. 



133 The form of the planetary body containing tlie solid matter of llio 

 comet is globnlar. 



133 The transparent conietic atmosphere is also globnlar. 



134 The envelope mnst have been an inverted hollow cone terminating 



at its vertex in an ei^nally hollow cap nc^arly hemispherical. 



134 This hemispherical cap was comparatively thin. 



135 The constrnction of the envelope explained. 



The luminous matter as it arises from the envelope, of which it is a 

 continuation, is thrown a little outwards and assumes the appear- 

 ance of two diverging bright streams; but if the source from 



136 which they rise bo the circular rim of a hollow hemispherical shell 

 the luminous matter in its progress upwards can only form a hol- 

 low cone. 



136 The feebler light of the tail between the streams is due to the thinness 

 of the matter in the middle of the hollow cone through which we look. 



136 Of the Solar agency in the production of Comctic Phenomena. 



137 As a comet ai>proaches perihelion it is [more] exposed to the action 



of the solar rays, which can produce light, heat, and chemical 

 eftects. Their influence on this comet has produced an expansion. 

 The way these effects have been produced may be supposed to have 

 been as follows : 

 137 The matter in the head of the comet would be dilated by The action 

 of the sun, chiefly in that hemisphere of the head nearest the sun : 

 and, being more increased in this direction than the other, it would 

 become eccentric when referred to the situation of the body of the 

 comet. The head being what draws our greatest attention, the 

 planetary body would appear eccentrically situated. 



137 The nebulous matter which, when the comet is far from perihelion, 



is probably spherical, would, near perihelion, be rarefied and rise 

 to a certain level. In this situation we have had an opportunity 

 of seeing the transparent atmosphere, which, but for the suspen- 

 sion of the nebulous matter, we might never have discovered. 



138 The brilliancy and color of the envelope are proofs of the continued 



action of the sun, and if we suppose the attenuation of the lumin- 

 ous matter, already very rare, to be carried on, its particles will 

 o-radually recede from the hemisphere exposed to the sun and 

 ascend towards the region of the flxed stars. Some such operation 

 mnst have been carried on. 



138 A whole heniisph(5re of it being exposed to the sun, it must ascend 



equally everywhere all round this and Ix^come a hollow cone. 

 1.39 The luminous matter ascending in the hollow cone received no addi- 

 tion to its rpiantity from any other source but the exposed hemi- 

 siihere. 



139 The tail, near the end, must have been rarefied in an extreme degree. 

 139 The vacancy occasioned by the escape of the nebulous matter was 



probably filled up, either from the opposite hemisphere or by a ro- 

 tation of the comet about an axis. 



139 That such a process took place seems to be supported by observation. 



140 A rotatory motion of the comet would explain the variation in the 



lengths of the two branches of the tail. 



