DESCRIPTION OF FRONTISPIECE. 1. A CONTINUOUS SPECTRUM, SUCH AS IS GIVEN BY THE LIGHT FROM SOLID, LIQUID, AND DENSELY GASEOUS BODIES WHEN IN A STATE OF INCANDESCENCE. 2-8. DISCONTINUOUS SPECTRA, SUCH AS ARE GIVEN BY THE LIGHT OF GASES OR VAPOURS WHEN INCANDESCENT. The examples chosen are :— 2. Sodium vapour. 3. Magnesium vapour, showing the lines due to the rarer and denser vapours. 4. Chloride of strontium, an example of the spectrum of a compound body, the finer lines in the blue-green being alone due to the metallic strontium. 5. Hydrogen at high pressure. 6. Hydrogen at low pressure. 7. Spectrum of a Nebula (Huggins). 8. Spectrum of the Sun's Chromosphere, tracing the bright lines to the radiation of sodium, hydrogen, &c. (Lockyer). 9, 10. EXAMPLES OF ABSORPTION :— 9. The Solar Spectrum, tracing the dark lines D, C, F, b, &c., to the absorption of sodium vapour, hydrogen, magnesium vapour, &c. 10. The absorption of sodium vapour, showing the coincidence of the bright line with the dark line D in the solar spec trum. 23 Ե LIST OF ILLUSTRATIONS. FAGE 2356 FIG. 1. Geometrical form of the prism. 2. Prism mounted on a stand 3. Refraction of light 4. Explanation of the bent stick 5. Refraction of light. Apparent elevation of the bottoms of vessels 6. Light passing through plate of glass 8. Images of objects seen through prisms 7890 ΙΟ 9. Decomposition of light by the prism. bility of the colours of the spectrum. Unequal refrangi 16. Spectroscope with reflected scale 17. Huggins's star spectroscope 10. Recomposition of white light by means of a second prism 12. Left-hand diagram, solar spectrum near D; right-hand dia- 13. Chemical or student's spectroscope 14. Spectroscope with two prisms 15. Steinheil's form of four-prism spectroscope: arrangement of slit shown separately. 18. Direct-vision prism with three prisms, showing path of ray 19. Direct-vision prism with five prisms 20. Electric lamp 21. Arrangement of the electric lamp used for rapid comparisons 22. Bunsen's burner for flame spectra. 39 42 23. Mitscherlich's arrangement for flame spectra 43 24. Herapath's blow-pipe. 25. Arrangement for determining the spectra of metals by means of the electric spark, showing induction coil, Leyden jar, and spark stand 44 25. The electric arc 27. Geissler's tube, showing electric discharge 46 47 48 58 33. Sun spectroscope arranged for photography 34. Automatic arrangement for securing the minimum deviation of the observed ray PAGE 59 60 63 35. Spectra of Aldebaran and a Orionis. (Huggins and Miller) 64 36. Spectrum of the nebula. 37. Ring nebula in Lyra, with its spectrum 38. Planetary nebula in Aquarius, with its spectrum 39. Views of Donati's comet 68 69 40. I, Spectrum of Brorsen's comet; 2, Spectrum of Winnecke's comet 3, Spectrum of carbon in olefiant gas; 4, Spectrum of carbon in olive oil. (Huggins) 41. The eclipsed sun, August 1869, showing the corona and prominences at a, b, c, d, e, f, g 42. Spectrum of the sun's photosphere and chromosphere 43. Cline bright in chromosphere, dark on sun 44. F line in chromosphere, showing widening near the sun 45. Method of observing the absorption of a vapour 46. Glass case for studying the absorption of liquids 47. Absorption spectra of iodine and nitrous fumes 48. Dark band in magenta and dark bands in blood 49. Steinheil's slit, showing reflecting prism. 70 72 75 76 77 81 82 83 84 93 93 50. Path of light through reflecting prism and into the slit 96 52. Correspondence of some of the lines given out by iron vapour, and of some of the Fraunhofer lines in the solar spectrum 97 53. A sun-spot (Secchi), showing the "straws" in the penumbra, and the irregular masses on the general surface 54. Spectrum of sun-spot (Young) 55. Spectrum of 7 Corona (Huggins) 56. Alteration of wave-length of the hydrogen in the atmosphere of Sirius 57. Deviation of the F line in a spot-spectrum 58. Shifting of the F line in a solar cyclone. 114 59. Prominence observed 14th March, 1869, 11h. 5m. 60. The same prominence, 11h. 15m. 116 117 THE SPECTROSCOPE AND ITS APPLICATIONS. LECTURE I. THE field of research which has been opened up by the spectroscope is one with which we have so recently become familiar, that it may almost be said that twenty years ago a course of lectures on the spectroscope would have been an impossibility. The instrument, as we now know it, was then only in embryo; and even at the present time, although immense strides are every day being made, the science of spectroscopy must still be considered in its infancy. And yet, so far as one can see nowit is always very easy to prophesy after the event -there seems very little reason why lectures on the spectroscope should not have been given two centuries ago; for nearly two centuries have elapsed since the immortal Newton made his classical reB S |