592 BIBLIOGRAPHY OF HEESCHEL's WRITINGS. 



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

 A. D. Vol. P. 



liavo an alternate reflection and transmission of them. If to get 

 over this objection it should be said that, instead of transmission, 

 we ought to substitute absorption ; since those which in glass would 

 have been transmitted will be absorbed by the metal, we may ad- 

 mit the elusion; it ought, however, to have been made apart of the 

 hypothesis." 

 1807 97 226-228 XXXI. Alternate Fits of easy Eejlcction and easy Transmission, if 

 they exist, do not exert themselves according to various Thicknesses 

 of thin Plates of Air. One end of a plain strip of glass rested 

 upon a plain metalline mirror, the other end being separated 

 from the mirror by a thin piece of paper. A lens resting upon 

 the strip of glass gave the primary set of rings, and the sec- 

 ondary set by transmission was seen reflected in the metalline 

 mirror. The rays which convey the secondary set of rings to 

 the eye must have passed through the thin wedge of air ; but 

 they exhibited no modification, hence the conclusion. 

 228-229 XXXII. Alternate Tits of ea'iy Eejleciion and easy Transmission, if 

 they exist, do not exert themselves according to various Thicknesses 

 of thin Plates of Glass. An experiment similar to the preceding, 

 but using a slip of glass with sides not quite parallel. 

 230-232 XXXIII. Coloured Pings may be completely formed tvithout the As- 

 sistance of any thin or tliick Plates, cither of Glass or of Air. 

 A perforated screen, at the center of curvature of a metal mirror, 

 transmitted a beam of sunlight to the mirror. When hair-powder 

 was strewn in the beam of light, coloured concentric circles were 

 seen abont the hole in the screen. 

 232-233 XXXIV. Conclusion. The experiments of the last three articles are 

 regarded as proofs that the theory of Sir Isaac Newton is untenable. 



1807 97 260 Observations on the Nature of the new celestial Body discovered by Dr. Ol- 



BERS, and of the Comet which was expected to appear last January in its 

 return from the sun. [This was comet, 1806, II.] By William Her- 

 SCHEL,LL. D., F. E. S. Eead June 4, 1807. 

 260 As soon as I knew of the discovery of [ Vesta'} I tried to discover its 

 situation. 



262 Observations of Vesta. 



263 No disc has been seen even with a power of 636. 



264 Observaiions of the expected comet. It was searched for and found near 



the expected place by my Sister Carolina, Jan. 27. 

 266 Out of 16 comets which I have examined 14 have been without any 



visible solid body in their centre, and two had a very ill-defined 



small central light which might perhaps bo called a nucleus, but 



which did not deserve the name of a disk. 

 266 Plate XVI. Configurations of Vesta and stars. 



1808 98 145 Observations of a Comet made with a view to investigate its Magnitude and 



the Nature of its Illumination. [This was comet, 1807, I.] To which 

 is added an Account of a new Irregularity lately ])crceired in the ap- 

 parent Figure of the Planet Saturn. By William Herschel, LL. D., 

 F. E. S. Eead April 7, 1808. 



145 My observations have been directed to its physical condition only. 



146 Of the Nucleus. By the nucleus, I mean that part of the head which 



appears to be a condensed or solid body, and in which none of the 

 very bright coma is included. It follows from this definition that 

 when the nTicleus is very small a largo, telescope is required to show it. 



