action could only be justified by necessity, and that it might very probably detract a good deal from the value and interest of the discussions following the papers. He hoped that all who felt with him in this matter would do their utmost to help in improving the financial position of the Institute so that they might soon be able to return to their former practice in this respect. The Rev. P. ROSE seconded the Resolution, which was carried unanimously. Mr. J. O. CORRIE proposed and the Rev. R. WRIGHT HAY seconded "That the Council and Officers named in the Report be elected, and that the thanks of the Meeting be passed to the retiring Members of Council, Mr. W. J. Horner and Dr. Heywood Smith, M.A." The Resolution was carried unanimously. The Right Rev. Bishop THORNTON proposed, and the Rev. JOHN TUCKWELL seconded "That the cordial thanks of this Meeting be passed to the Vice-President, Mr. David Howard, D.L., F.C.S., for presiding on this occasion." The Resolution was carried unanimously. The CHAIRMAN, in acknowledging the vote, said:" It is a great pleasure to be present at the Annual Meeting of the Victoria Institute. I have watched its work for many years, and am more and more convinced of the soundness of its principles. "We still need, perhaps more than ever, a patient and careful investigation of new problems to see what is really the truth; and experience shows that a seeming contradiction to what we believe may be really no contradiction at all. Take, for instance, Evolution : fortuitous Evolution is given up and we hear of the laws of Evolution; where there is a law there must be a lawgiver, and we are back on the old ground, and with a change of statement. Paley's arguments hold still. Above all, let us beware of asking despairingly with Pilate, 'What is Truth?' If only he could have known that the answer was the Man Who stood before him." The Meeting closed at 4.30 p.m. 565TH ORDINARY GENERAL MEETING, HELD IN THE CONFERENCE HALL, THE CENTRAL HALL THE REV. PREBENDARY H. E. Fox OCCUPIED THE CHAIR AT The Minutes of the preceding Meeting were read and confirmed. The SECRETARY announced the election of the Rev. Martin Anstey, M.A., B.D., and of the Rev. George Campbell Morgan, D.D., as Members of the Institute. The CHAIRMAN, the Rev. Prebendary Fox, invited Professor Alfred Fowler, F.R.S., Secretary of the Royal Astronomical Society, and Professor of Physics in the Royal College of Science, to address them on the subject of "The Spectra of Stars and Nebula." The lecture was illustrated throughout by lantern slides. IN THE SPECTRA OF STARS AND NEBULÆ. N this lecture it will be my endeavour to give some indication of the way in which the wonderful power of the spectroscope has been utilized in investigations of the chemistry of stars and nebulæ, and of the bearing of such knowledge on the question of celestial evolution. The only intelligible message that a star sends to the earth is borne on its rays of light, and if we are to learn anything at all of the composition and physical state of the star, it must be by the analysis of that light. The spectroscope is an instrument which enables us to make such an analysis, by taking advantage of the dispersive power of a prism or diffraction grating, whereby a complex beam of light is separated into its component parts. Before we can understand the language of the spectroscope it is necessary to study very carefully the sources of light which can be artificially produced. If we examine the light from an incandescent solid body, such as a gas mantle or the filament of a glow lamp, we find that the spectroscope spreads it out into a band showing the glorious colours of the rainbow in their greatest purity. The colours from red to violet merge into each other by insensible gradations, and we say that the spectrum is a continuous one, because there are no interruptions of any kind. All incandescent solid bodies give precisely the same result, and it follows that we cannot distinguish between one luminous substance and another so long as they remain in the solid state. The same is true of incandescent liquids. The effects are very different when the substances examined are in the state of luminous gas or vapour. They then emit special kinds of light by which they can be identified, and it does not matter in the least whether they are in our laboratories or far away in the depths of space, so long as their light reaches our instruments with sufficient intensity. The spectra are no longer continuous, but consist of a number of bright lines of different colours, which are really a succession of images of the narrow slit through which the light is admitted to the spectroscope. Thus, hydrogen is characterized by a line in the red, another in the blue-green, and others in the blue and violet, and since these lines are exhibited by nothing but hydrogen, they serve to indicate the presence of hydrogen wherever it occurs in the luminous state. Similarly, helium signifies its presence by a number of lines, of which one in the yellow is especially conspicuous. Each of the other elements also has its own distinctive family of spectrum lines, some consisting of a few members only, but others, such as iron, occurring in hundreds. Many compounds which can be excited to luminosity without decomposition also exhibit characteristic spectra, which are quite different from those of the elements of which they are composed. The luminosity necessary for spectroscopical analysis may be artificially produced in various ways. Gases are usually enclosed in vacuum tubes containing the gases at reduced pressures, and are illuminated by electrical discharges. Substances which are solid at ordinary temperatures may be vaporized and rendered luminous by the oxy-hydrogen flame, the electric arc, the electric spark, and in a variety of other ways which need not now be specified. It is most important to study the spectra in as many different ways as possible, because, in opposition to early ideas, it has been found that the same substance may give different spectra when excited in different ways. Thus, at flame temperature, or under the action of gentle electric discharges, many substances give spectra consisting of broad bands, or flutings, such bands consisting of a multitude of very fine lines closely packed together. At the higher temperature of the electric arc these bands are replaced by lines which occupy quite different positions in the spectrum. Further modifications, involving the weakening of some lines appearing in the flame or arc, the brightening of others, or even the appearance of new lines, are often found when the substance is submitted to the violent action of the condensed electric discharge. Lines which are intensified, or only appear under spark conditions, have been called " enhanced lines," and it is by the study of such lines, initiated by Sir Norman Lockyer, that much of the recent progress in the interpretation of solar and stellar spectra has been due. We see, then, that the same substance may give widely different spectra under different experimental conditions, but the spectrum is nevertheless always the same under the same conditions, and no two substances ever give the same spectrum. This multiplicity of spectra might at first sight appear to be an undesirable complication in spectrum analysis, but in reality it enormously increases the interest of observations of the celestial bodies, because it enables us to learn something of the physical conditions which prevail as well as of their chemical constitution. We do not yet know the precise cause of the variations in the spectrum of a substance, but it is generally believed that, while band spectra are produced by the vibrations of molecules, or of electrons which form part of molecular systems, line spectra are only produced when the applied energy is sufficient to break up the molecules into atoms. As to the change in the line spectrum which is often observed on passing from the arc to the spark spectrum, modern theories of atomic structure suggest that further dissociation takes the form of the removal of one or more electrons from each of the atoms involved. Whatever the ultimate cause may be, we do know that the change from bands to lines, and from ordinary flame to arc lines, and again from arc to enhanced (spark) lines, accompanies the application of greater energy to the molecules and atoms, whether it be in the form of heat or electricity. So far, reference has been made to emission spectra only. Kirchhoff's famous experiment of 1859 proved that a luminous vapour has the property of absorbing precisely the same kind of light that it emits, so that if such a vapour lies in front of a source at higher temperature giving a continuous spectrum, the result is a continuous spectrum crossed by dark lines. This is called an absorption spectrum, and Kirchhoff's observation is of fundamental importance in astronomy, because the spectrum of the sun and the spectra of nearly all the stars show dark lines on a bright, continuous background. The experiment shows that we can identify the substances which produce such dark lines, just as surely as if they were bright, by the process of matching them by emission spectra artificially produced. Such, then, are the main principles of spectrum analysis. We may next consider their application to celestial bodies, beginning with the sun, which may properly be regarded as the nearest star. The dark lines which are characteristic of the spectrum of sunlight were first accurately mapped by the German physicist Fraunhofer in 1814, and have since been known as the Fraunhofer lines. In more recent times the magnificent photographs obtained by Rowland exhibit not less than 20,000 of these lines, which have been carefully entered in a great catalogue, showing their relative intensities and their positions on the scale of wave-lengths of the vibrations which produce them. The chemical significance of a great number of these lines has been determined by the application of Kirchhoff's principle of the reversal of lines, by Kirchhoff himself, and subsequently by Lockyer, Rowland, and others. The great majority of the more prominent lines have, in fact, already been matched by spectra produced in the laboratory, largely from common substances such as hydrogen, sodium, magnesium, iron, and calcium. In accordance with Kirchhoff's experiment, we interpret the dark lines of the solar spectrum as indicating that the bright central ball of the sun-which of itself would give a continuous spectrum is surrounded by luminous gases and vapours which produce the dark lines by their absorption. At ordinary times this atmosphere is not visible, because it is not so bright as the diffused light of the sky, but its existence is fully confirmed by observations during total eclipses of the sun, when the glare of the surrounding sky is shut off by the moon's shadow. Under these conditions the direct emission spectrum of the sun's atmosphere may be observed or photographed. In place of the usual dark Fraunhofer lines the expected multitude of bright lines is then observed in the spectrum at the sun's edge during the few seconds that this comparatively shallow "reversing layer" or "flash stratum" remains uncovered by the moon. It |