elliptic sector, areas of roulettes, the theory of Amsler's planimeter, Landen's theorem on the length of a hyperbolic arc, Steiner's theorem on the rectification of roulettes, and some others. It will be seen, from this brief account of the contents, that the work is of a strictly elementary character. Such subjects as the expansion of functions in trigonometrical series, elliptic functions, and the Calculus of Variations are simply omitted; while the transformation of the independent variable and double integration are but briefly noticed. Within the limits which the author has assigned to himself, however, the treatment is very full and satisfactory; and the work is well adapted to the wants of those for whom it is written, viz. students in the Universities, very few of whom (as we suppose) will find it necessary to enter into the subject beyond the contents of the present volume. XXXVI. Proceedings of Learned Societies. ROYAL SOCIETY. [Continued from p. 237.] June 11, 1874.-Joseph Dalton Hooker, C.B., President, in the Chair. THE following communications were read: "Spectroscopic Notes.-No. III. On the Molecular Structure of Vapours in connexion with their Densities." By J. Norman Lockyer, F.R.S. 1. I have recently attempted to bring the spectroscope to bear upon the question whether vapours of elements below the highest temperatures are truly homogeneous, and whether the vapours of different chemical elements, at any one temperature, are all in a similar molecular condition. In the present note, I beg to lay before the Royal Society the preliminary results of my researches. 2. We start with the following facts: I. All elements driven into vapour by the induced current give line-spectra. II. Most elements driven into vapour by the voltaic arc give us the same. III. Many metalloids when greatly heated, some at ordinary temperatures, give us channelled-space spectra. IV. Elements in the solid state give us continuous spectra. 3. If we grant that the spectra represent to us the vibrations of different molecular aggregations (this question is discussed in Note II.), spectroscopic observations should furnish us with facts of some importance to the inquiry. 4. To take the lowest ground. If, in the absence of all knowledge on the subject, it could be shown that all vapours at all stages of temperature had spectra absolutely similar in character, then it would be more likely that all vapours were truly homogeneous and similar among themselves, as regards molecular condition, than if the spectra varied in character, not only from element to element, but from one temperature to another in the vapour of the same element. 5. At the temperature of the sun's reversing layer, the spectra of all the elements known to exist in that layer are apparently similar in character-that is, they are all line-spectra; hence it is more probable that the vapours there are truly homogeneous, and that they all exist in the same molecular condition, than if the spectrum were a mixed one. 6. The fact that the order of vapour-densities in the sun's atmosphere, which we can in a measure determine by spectroscopic observations, does not agree with the order of the modern atomic weights of the elements, but more closely agrees with the older atomic weights, led me to take up the present research. Thus I may mention that my early observations of the welling-up of Mg vapour all round the sun above the Na vapour have lately been frequently substantiated by the Italian observers; so that it is beyond all question, I think, that, at the sun, the vapour-density of Mg is less than that of Na. 7. The vapour-densities of the following elements have been experimentally determined : :- 8. To pursue this inquiry the following arrangements have been adopted :— The first experiments were made last December upon Zn in a glass tube closed at each end with glass plates; and I have to express my obligations to Dr. Russell for allowing them to be conducted in his laboratory, and for much assistance and counsel concerning them. A stream of dry H was allowed to pass. The tube was heated in a Hofmann's gas-furnace, pieces of the metal to be studied having previously been introduced. It was found that the glass tube melted; it was therefore replaced by an iron one. The inconvenience of this plan, however (owing to the necessity for introducing the metal into the end of the hot tube when the first charge had volatilized), and, moreover, the insufficiency of the heat obtainable from the gas-furnace, soon obliged me to replace both tube and furnace by others, which have now been in use for many weeks, and which still continue to work most satisfactorily. The iron tube is 4 feet in length, and is provided with a central enlargement, suggested to me by Mr. Dewar, forming a T-piece by the screwing in of a side tube, the end of which is left projecting from the door in the roof of the furnace. Caps are screwed on at each end of the main tube; these caps are closed by a glass plate at one end, and have each a small side tube for the purpose of passing hydrogen or other gases through the hot tube. The furnace is supplied with coke or charcoal; an electric lamp, connected with thirty Grove's cells, is placed at one end of the tube and a one-prism spectroscope at the other. The temperatures reached by this furnace may be conveniently divided into four stages: I. When the continuous spectrum of the tube extends to the sodium-line D, this line not being visible. II. When the continuous spectrum extends a little beyond D, this line being visible as a bright line. III. When the spectrum extends into the green, D being very bright. IV. When the spectrum extends beyond the green and D becomes invisible as a line, and the sides of the furnace are at a red heat. I may add (1) that I have only within the last few days been able to employ the third and fourth stages of heat, as the furnace was previously without a chimney, and the necessary draught could not be obtained; and (2) that I was informed, a little time ago, by Prof. Roscoe that, with a white-hot tube, he had observed new spectra in the case of Na and K. These spectra, which I now constantly see when these temperatures are reached, I shall call the " new spectra." 9. The results of the experiments, so far as the visible spectrum is concerned, between the stages indicated may be stated as follows: H. No absorption. N. No absorption. K. I have observed, either separately or together : (a) The line absorption-line near D. (3) Continuous absorption throughout the whole spec trum. (7) Continuous absorption in red and blue at the same time, the light being transmitted in the centre of the spectrum (as by gold-leaf). (8) Continuous absorption clinging on one side or other of the line. (This phenomenon, which, so far as I know, is quite new, will be described in another note.) (e) The new spectrum. Na. I have observed, either separately or together:- (B) Continuous absorption throughout the whole spec trum. (7) Continuous absorption clinging on one side or the other of D. (d) The new spectrum. H K Zn. Continuous absorption in the blue. (An unknown line sometimes appears in the green, but certainly no line of Zn.) Cd. Continuous absorption in the blue. Sb. New spectrum, with channelled spaces and absorption in P. The same. (This, however, in consequence of the ex- be repeated.) Bi. No absorption. I. Channelled spectrum in the green and intense bank of general absorption in the violet, where at the ordinary temperature the vapour transmits light. Hg. No absorption. 10. These results may be tabulated as follows:— As.... 150 75 P 62 31 Na (?) 23 Zn (?) 65 Sb (?) 122 Hg.. 100 .... 32 208 Channelled-space spectrum probable. Continuous absorption in the violet. 11. It will be seen from the foregoing statement that if similar spectra be taken as indicating similar molecular conditions, then the vapours, the densities of which have been determined, have not been in the same molecular condition among themselves. Thus the vapours of K, S, and Cd, at the fourth stage of heat, gave us line, channelled-space, and continuous absorption in the blue respectively. This is also evidence that each vapour is non-homogeneous for a considerable interval of time, the interval being increased as the temperature is reduced. "Spectroscopic Notes.-No. IV. On a new Class of Absorption Phenomena." By J. Norman Lockyer, F.R.S. 1. In the experiments on the absorption-spectrum of Na and K vapour heated in a red-hot tube, to which further reference is made in separate notes, I have observed phenomena quite new to me, some rough drawings of which I lay herewith before the Royal Society. As the phenomena are only momentary, I cannot answer for the final accuracy of the drawings, nor have I been able to represent the softness of the gradations of shade. 2. In the drawings, the red end of the spectrum is to the left; the D line common to them all is the image of a slit about half an inch long, on which slit the light falls from an electric lamp, through the tube and chamber in which the vapours are produced. The lower part of the drawings would generally represent, therefore, the spectrum of the less dense vapours were the vapours at rest. 3. One of the phenomena referred to consists of what may be described as a unilateral widening of the line D: the side absorption, however, is much less dense than that of the line; it is bounded by D on one side and by a curved line on the other. Figs. 1, 2, and 3 will give an idea of this appearance in three stages as it is frequently actually seen, i. e. as the absorption travels up or down the line it widens as shown. 4. Figs. 4 and 5 give two variations sometimes observed-fig. 4 showing the darkening in the absorption and an increased steepness in the curve; fig. 5 the simultaneous existence of apparently different absorptions, all bounded by D on one side, but by different curves on the other, and being of different intensities. |