538 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herscliel, W.: Synopsis of the Writings of— Continuecl. 



A. D. Vol. p. 



of the stars od the wall, the moveable wire may be set to the par- 

 allel of the large star, which will give the angle of position pretty 

 accurately. 



1785 75 78 Third Class of Double Stars. [iNos. 47 to 114,] 



82 [Foot-note. ] With regard to small stars that become visible by an in- 



crease of magnifying power, we may surmise that it is partly owing 

 to the greater darkness of the field of view arising from the increased 

 power, and jiartly to the real effect of the power. 



83 [Foot-note.] The prismatic power of the atmosphere, of which little 



notice has been taken by astronomers, is that part of its refractive 

 quality whereby it disperses the rays of light and gives a lengthened 

 and colored image of a lucid point. It is very visible in low stars; 

 ' Fomalhaut, for instance, affords a beautiful prismatic spectrum [ex- 



periments given], which explain also why a star is not always best 

 in the center of the field of view ; a fact I have often noticed before 

 I knew the cause. 

 91 Fourth Class of Double Stars. [Nos. 45 to 132.] 

 105 Fifth Class of Double Stars. [Nos. 52 to 137.] 

 118 Sixth Class OF Double Stars. [Nos. G7 to 126.] 

 126 Additional Errata to the Catalogue of Double Stars, Phil. Trans., vol, 



Ixxii. 

 126 Plate V gives figures of 44 Lyncis and /j. Aurigce. 



1785 75 213 On the Construction of the Heavens. By William Herschel, Esq., F. 

 R. S. Read Feb. 3, 1785. 



213 In an investigation of this delicate nature we ought to avoid two op- 



jjosite extremes. If we indulge a fanciful imagination and build 

 worlds of our own, we must not wonder at our going wide from the 

 path of truth and nature. On the other hand, if we add observa- 

 tion to observation, without attempting to draw not only certain 

 conclusions but also conjectural views from them, we offend against 

 the very end for which only observations ought to be made. I will 

 endeavor to keep a proper medium, but if I should deviate from that, 

 I could wish not to fall into the latter error. 



214 Theoretical view of the formation of nebulae. 



Form I. Condensation of neighboring stars about a central and larger 

 star ; globular forms. 



215 Form II. Condensation of neighboring stars about a nucleus of con- 



tiguous stars ; condensed irregular forms. 

 Form III. Condensation about a stream of stars, producing a form 

 coarsely similar to the prototype : extended, branching, compound 

 forms. 



216 Form IV. Compound forms derived from the mutual attraction of 



clusters. 



V. Vacancies will then arise in the surrounding space. 



Objection to the above views ; they tend to show a gradual destruc- 

 tion of the universe. Response, that space is infinite and that the 

 occasional destruction of one star may operate to give life to the 

 rest. 



217 Optical appearances to an observer within a nebula of the third form. 

 219 Results of observation — star gauges. 



221-240 Gauges throughout the 24*^ in R. A. Results given in detail in a 

 Table. 



