LECTURE VI.

Stellar Chemistry.-Huggins and Miller.-Spectra of the Fixed Stars. -Difficulties of Observation.--Methods employed.--Variable Stars.-Double Stars.-Temporary Bright Stars.-Nebula.Comets. Conclusion.

Appendix A.-Extract from a Memoir "On the Spectra of some of the Fixed Stars."

Appendix B.-" On the Spectrum of Mars, with some Remarks on the Colour of that Planet."

Appendix C.-"On the Spectra of Variable Stars."

Appendix D.-"Further Observations on the Spectra of some of the Stars and Nebula, with an Attempt to determine therefrom whether these Bodies are moving towards or from the Earth; also Observations on the Spectra of the Sun and of Comet II. 1868."

In the last lecture I endeavoured to point out to you the principles upon which Professor Kirchhoff arrived at the remarkable conclusion that certain metals well known on earth are contained in the solar atmosphere. I have to-day to bring before you facts which are still more interesting, with regard to the chemical composition of the stars and the nebulae; and if in the former lectures I had to couple the names of two great German philosophers, I have to-day to bring before your notice the researches of two distinguished Englishmen-Mr. Huggins and Dr. Miller-to whom we are indebted for almost all our knowledge of stellar chemistry.

Although the moon and planets, shining by borrowed light, do not reveal to the spectroscope the nature of the

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Wo, labá, he owered the of a star at the moment te qark edge of the man passed over in K an atmosphere extered in the moon, the cleerver wald the starlight by refraction after the occultation had geored just as the setting son is visible to us after it has actually disappeared below the horizon. The variously coloured rays are, however, differently refrangible; and if any atmosphere existed round the moon, the red rays being least so would die out woonest, and the spectrum of the star would be seen progressively to diminish in intensity, beginning from the red end. Mr. Huggins observed nothing of this kind, all the rays of the stellar spectrum disappearing simultaneously: and the conclusion must be drawn that the moon is devoid of any appreciable atmosphere.

In the spectrum of Jupiter lines are seen which indicate the existence of an absorptive atmosphere about this planet. These lines plainly appeared when viewed simultaneously with the spectrum of the sky, which at