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July 11,1862.] THE PHOTOGRAPHIC NEWS. 327 hydrogen. sodium. magnesium and iron. strontium and iron (uncertain). iron. calcium. „ C „ D „ B „ F , G The 2 lines H The remainder of Angstrom’s paper goes into theoretical and mathematical discussions on the theory of the reciprocity of radiation and absorption, and of the theory of thermometric heat, those of our readers who care to pursue this interesting subject in its further details, will do well to refer to the entire paper which will be found at length in this month’s number of the Philosophical Hag azine. Some interesting experiments have been lately tried by Dr. Frankland on the temperature at which coal gas ignites. The heterogeneous mixture of gases and vapour known as coal gas may for this purpose be assumed to consist of— olefiant gas and other luminiferous hydro-carbons, light carburetted hydrogen or fire damp, hydrogen, carbonic oxide, and bi-sulphide of carbon, as under certain circum stances these gases can become separated to some extent, it was thought advisable to examine separately their res pective igniting points. Olefiant gas required to inflame it, the heat of an iron which appeared of a cherry red colour in diffused daylight. Light carburetted hydro gen can be inflamed by white shot sparkling iron, but not by iron at a red heat; it is, therefore, less inflammable than hydrogen, carbonic oxide, or olefiant gas. Hydrogen requires for its ignition, an iron heated to a temperature beyond visible redness in a tolerably well lighted room. Carbonic oxide inflames at a little higher temperature that that required to set fire to hydrogen. Bi sulphide of carbon vapour was found to ignite at as low a temperature as 300° F. Owing to the law of the diffusion of the distance between 11 and Cr, and that nearest to G is double, as belonging also to calcium. Moreover, at G, and in its immediate neighbourhood towards F, wo have five strong, besides eight fainter lines; at F, again, five; and lastly, around E, a numerous group, all answering to dark lines in the solar spectrum. An additional fact is also given respecting magnesium; the third of the lines, marked b, reckoning towards F, is double, and belongs, accordingly, both to magnesium and iron. The existence of four bodies in the sun has been shown by Kirchhoff'; and to these, Angstrom now proposes to add calcium, aluminium, and man ganese, and also, in all probability, strontium and barium. Calcium has three strong lines at the violet end of the spec trum, of which two are especially remarkable as being identical with the well known pair of lines H, and the third in order forms, with one of the iron lines, the strong double line mentioned above. Calcium has also several lines in other parts of the spectrum, all of which have their counter parts in that of solar light. Aluminium is also characterized by two strong lines lying between the H lines of the solar spectrum, and there corresponding to two dark lines. Man ganese gives a spectrum which very much resembles that of iron ; the different groups between G and H, and thirteen manganese lines between G and F, closely approach similar ones in the iron spectrum, and are also identical with cor responding lines of the solar spectrum. Strontium has two strong lines between F and G, which apparently correspond to solar lines, and this also seems to be the case with the line F. It must, however, be mentioned, that the presence of stron tium in the sun is very uncertain, owing to the very brilliant blue line which this metal shows between F and G, having no corresponding line in the solar spectrum. Barium has four lines between F and D, which seem to have their counterparts in the solar spectrum ; this also requires con firmation. To give in a general view the principal coincidences between the Frauenhofer lines and those in the artificial metallic spectra, we have the following general view :— The line B belongs to potassium. Stientifit Gossiy. DIscovEnY or New Metals in the Sun, Calcium, Alu- smiuk, and Magnesium—Identification of FRAUENMIOFER’s Lines—Igniting Point of Coal Gas. Since we last reported on the subject of the solar spectrum, Mme very interesting as well as important researches have wen published by Angstrom which led to some further conclusions respecting the composition of the solar photo sphere. It may, he considers, be taken for granted that the Frauenhofer lines for the most part originate in the sun’s photosphere, or the gaseous envelope that immediately surrounds that body. As an objection to this hypothesis, it has been urged that the lines in that case ought to appear stronger and more distinct when the rays come from the centre of the disc. According to an oft quoted observation of Professor Forbes thishas not been thought correct. Forbes’ observation, however, took place during the occurrence of a tolar eclipse, under which circumstances it would be very difficult to preserve the appearance of the spectrum ac curately in the memory. Angstrom therefore considered that the experiment was worth repeating. He used for this Purpose an optical theodolite with two telescopes, one of *hieh was furnished with a slit-opening to admit the sun light. The height of this aperture was reduced very considerably, and the sun’s imago was projected upon it bom a Dolland object glass of about ten feet focus. The diameter of the image thus formed was about an inch : and by allowing the rays from different parts of this image to fell successively upon the opening, it was easy to see whether the Frauenhofer lines underwent any change. No very Bemarkable difference was perceptible; all that could be noticed was, that the intensity of the spectrum light is Bomewhat less when the ray comes from the edge than when bom the centre of the disc; this being evidenced by the circumstance that the fainter Frauenhofer lines show them- fi elves in the latter case comparatively stronger, whereas When the light comes from the centre of the solar disc, the fainter lines will sometimes even totally disappear, while the stronger lines, some of the iron lines for example, Appear with correspondingly increased brilliancy : thisobser- xation is not repugnant to what we already know concerning the absorbing power of gases, and does not, therefore, militate ’gainst the hypothesis of the metallic composition of the 'la's atmosphere. Angstrom has verified Kirchhoff’s state- nents respecting the coincidence between the lines of iron, "agnesium, nickel, and the chromium, and corresponding Des in the sun’s spectrum. The iron lines identified by Bstrm are not quite so numerous as affirmed by Kirch- ij but are quite sufficient to establish beyond a doubt presence of iron in the solar atmosphere. These lines A the most characteristic in the whole solar spectrum : and Insufficient magnifying power be employed, or the light 7 refracted through more than one prism, the stronger °es among them appear perfectly black. u has been further remarked, that the lines belonging to air or to the gas through which the electric spark passes ’’hen working with an induction coil, are less distinct, and Wider, in proportion as the strength of the electricity is "oreased; whereas, the lines belonging to metals, especially ren somewhat refractory, like iron, remain perfectly sharp 'reler these circumstances. The metal lines may also be ' 'dmguished, in some measure, in the solar spectrum, when lammed with adequate magnifying power ; with moderate "Oy5n, certain lines appear somewhat prominent, and im- asIded 48 it were, in a mass of fine lines, which, upon the IP ication of increased illumination, appear to withdraw onmselves, and disappear, while the first-mentioned lines, metnes ontraiy, only stand out in stronger relief. These are invannes, and the most remarkable among them almost fifteaby belong to iron. Thus, between II and G we have the s18 ronger iron-lines, all having their counterparts in w spectrum. The two strongest of these lie | and 2